|**Stock-Based Compensation (Tables)**                                              | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
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|**Share-based Compensation Arrangement by Share-based Payment Award [Line Items]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Summary Of PSU Transactions                                                        | ﻿﻿﻿
				
				
				Number
				
				Weighted﻿
				
				
				of
				
				Average﻿
				
				
				Share Units
				
				Fair Value﻿Nonvested share units at beginning of period
				
				
				452,333
				
				$
				26.16﻿Granted
				
				
				87,593
				
				
				37.65﻿Performance criteria adjustment
				
				
				9,505
				
				
				31.89﻿Forfeited
				
				
				(7,780)
				
				
				30.61﻿Share units vested in prior period and issued in current period
				
				
				9,400
				
				
				26.54﻿Share units issued
				
				
				(136,081)
				
				
				31.70﻿Nonvested share units at end of period
				
				
				414,970
				
				
				26.83﻿
		﻿                                                                                      
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|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Nonvested share units at beginning of period                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Granted                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Performance criteria adjustment                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Forfeited                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Share units vested in prior period and issued in current period                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Share units issued                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Nonvested share units at end of period                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Summary Of RSU Transactions                                                        | ﻿﻿﻿
				
				
				Number
				
				Weighted﻿
				
				
				of
				
				Average﻿
				
				
				Stock Units
				
				Fair Value﻿Nonvested stock units at beginning of period
				
				
				116,787
				
				$
				29.46﻿Granted
				
				
				54,073
				
				
				34.91﻿Stock units vested in prior period and issued in current period
				
				
				1,467
				
				
				31.47﻿Stock units vested and issued
				
				
				(42,836)
				
				
				26.39﻿Forfeited
				
				
				(322)
				
				
				34.91﻿Nonvested stock units at end of period
				
				
				129,169
				
				
				32.77
		﻿                                                                                                                                                       
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
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|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Nonvested stock units at beginning of period                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Granted                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Stock units vested in prior period and issued in current period                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Stock units vested and issued                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Forfeited                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Nonvested stock units at end of period                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Assumptions Used In The Pricing Model                                              | ﻿﻿
				
				2018
				
				2017﻿Expected term (years)
				
				5.46
				
				5.45﻿Risk-free interest rate
				
				2.72%
				
				2.01%﻿Expected volatility
				
				17.2%
				
				17.7%﻿Dividend yield
				
				2.37%
				
				2.51%﻿Grant date fair value per option
				$
				5.10
				$
				4.07
		﻿                                                                                                                                                                                                                                                                                                                                                                                                                                            
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Expected term (years)                                                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Risk-free interest rate                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Expected volatility                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Dividend yield                                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Grant date fair value per option                                                  | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Summary Of Stock Option Transactions                                               | ﻿﻿﻿
				
				
				
				Weighted
				
				Weighted﻿
				
				
				
				Average
				
				Average
				
				Aggregate﻿
				
				
				
				Exercise
				
				Remaining
				
				Intrinsic﻿
				
				Shares
				
				Price
				
				Life (years)
				
				Value﻿Outstanding at beginning of period
				
				364,932
				
				$
				19.83﻿Granted
				
				160,859
				
				
				34.51﻿Forfeited
				
				(4,489)
				
				
				31.92﻿Expired / Cancelled
				
				(107)
				
				
				30.47﻿Exercised
				
				(63,099)
				
				
				16.14﻿Outstanding at end of period
				
				458,096
				
				$
				25.37
				
				5.9
				
				$
				4,494﻿﻿Exercisable at end of period
				
				225,117
				
				$
				17.23
				
				2.4
				
				$
				4,040
		﻿
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
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|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Outstanding at beginning of period                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Granted                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Forfeited                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Expired / Cancelled                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Exercised                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Outstanding at end of period                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Exercisable at end of period                                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Performance Share Units [Member]                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|**Share-based Compensation Arrangement by Share-based Payment Award [Line Items]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Summary Of Compensation Costs                                                      | ﻿﻿﻿
				
				Three Months Ended
				
				Six Months Ended﻿
				
				June 30,
				
				June 30,﻿
				
				2018
				
				2017
				
				2018
				
				2017﻿Stock-based compensation within operations and maintenance expenses
				
				$
				1,339
				
				$
				971
				
				$
				2,198
				
				$
				1,841﻿Income tax benefit
				
				
				373
				
				
				394
				
				
				614
				
				
				747
		﻿                                                                                                                                                                                                                                                                                                                                        
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Stock-based compensation within operations and maintenance expenses               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Income tax benefit                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Restricted Stock Units [Member]                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|**Share-based Compensation Arrangement by Share-based Payment Award [Line Items]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Summary Of Compensation Costs                                                      | ﻿﻿﻿
				
				Three Months Ended
				
				Six Months Ended﻿
				
				June 30,
				
				June 30,﻿
				
				2018
				
				2017
				
				2018
				
				2017﻿Stock-based compensation within operations and maintenance expenses
				
				$
				355
				
				$
				322
				
				$
				706
				
				$
				603﻿Income tax benefit
				
				
				100
				
				
				133
				
				
				201
				
				
				249
		﻿                                                                                                                                                                                                                                                                                                                                              
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
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|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Stock-based compensation within operations and maintenance expenses               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Income tax benefit                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Stock Options [Member]                                                             |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|**Share-based Compensation Arrangement by Share-based Payment Award [Line Items]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Summary Of Compensation Costs                                                      | ﻿﻿﻿
				
				Three Months Ended
				
				Six Months Ended﻿
				
				June 30,
				
				
				June 30,﻿
				
				2018
				
				2017
				
				2018
				
				2017﻿Stock-based compensation within operations and maintenance expenses
				
				$
				154
				
				$
				74
				
				$
				248
				
				$
				104﻿Income tax benefit
				
				
				42
				
				
				33
				
				
				101
				
				
				125﻿
		﻿                                                                                                                                                                                                                                                                                                                                           
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Stock-based compensation within operations and maintenance expenses               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Income tax benefit                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Stock Awards [Member]                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|**Share-based Compensation Arrangement by Share-based Payment Award [Line Items]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Summary Of Compensation Costs                                                      | ﻿﻿﻿
				
				Three Months Ended
				
				Six Months Ended﻿
				
				June 30,
				
				June 30,﻿
				
				2018
				
				2017
				
				2018
				
				2017﻿Stock-based compensation within operations and maintenance expenses
				
				$
				140
				
				$
				131
				
				$
				280
				
				$
				262﻿Income tax benefit
				
				
				41
				
				
				54
				
				
				81
				
				
				109
		﻿                                                                                                                                                                                                                                                                                                                                                 
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Stock-based compensation within operations and maintenance expenses               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Income tax benefit                                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Summary Of Nonvested Share Activity                                                | ﻿﻿﻿
				
				Number
				
				Weighted﻿
				
				of
				
				Average﻿
				
				Stock Awards
				
				Fair Value﻿Nonvested stock awards at beginning of period
				
				-
				
				$
				-﻿Granted
				
				8,099
				
				
				34.58﻿Vested
				
				(8,099)
				
				
				34.58﻿Nonvested stock awards at end of period
				
				-
				
				
				-
		﻿                                                                                                                                                                                                                                                                                                                                                                                              
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
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|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Nonvested stock awards at beginning of period                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Granted                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Vested                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|﻿Nonvested stock awards at end of period                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     

X- DefinitionTabular disclosure of the allocation of equity-based compensation costs to a given line item on the balance sheet and income statement for the period. This may include the reporting line for the costs and the amount capitalized and expensed.
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