|**Stock-Based Compensation (Tables)**                                              | 3 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
				
				
				443,410
				
				$
				27.20﻿Granted
				
				
				-
				
				
				-﻿Performance criteria adjustment
				
				
				(70,064)
				
				
				33.56﻿Forfeited
				
				
				(668)
				
				
				34.21﻿Share units issued
				
				
				(89,324)
				
				
				52.39﻿Nonvested share units at end of period
				
				
				283,354
				
				
				17.67﻿
		﻿                                                                                                                                                                                                 
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|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|﻿Nonvested share units at beginning of period                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|﻿Granted                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|﻿Performance criteria adjustment                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|﻿Forfeited                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|﻿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
				
				
				130,085
				
				$
				33.13﻿Granted
				
				
				55,489
				
				
				36.01﻿Stock units vested and issued
				
				
				(40,029)
				
				
				32.88﻿Forfeited
				
				
				(177)
				
				
				35.23﻿Nonvested stock units at end of period
				
				
				145,368
				
				
				34.30
		﻿                                                                                                                                                                                                                                                         
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|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|﻿Nonvested stock units at beginning of period                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|﻿Granted                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|﻿Stock units vested and issued                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|﻿Forfeited                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|﻿Nonvested stock units at end of period                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Assumptions Used In The Pricing Model                                              | ﻿﻿
				
				2019
				
				2018﻿Expected term (years)
				
				5.47
				
				5.46﻿Risk-free interest rate
				
				2.53%
				
				2.72%﻿Expected volatility
				
				17.7%
				
				17.2%﻿Dividend yield
				
				2.44%
				
				2.37%﻿Grant date fair value per option
				$
				5.25
				$
				5.10
		﻿                                                                                                                                                                                                                                                                                                                                                                                                                                      
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|﻿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
				
				422,972
				
				$
				25.97﻿Granted
				
				768,413
				
				
				35.94﻿Forfeited
				
				(1,696)
				
				
				34.78﻿Expired / Cancelled
				
				-
				
				
				-﻿Exercised
				
				(77,479)
				
				
				15.16﻿Outstanding at end of period
				
				1,112,210
				
				$
				33.60
				
				8.9
				
				$
				3,160﻿﻿Exercisable at end of period
				
				208,476
				
				$
				25.01
				
				5.4
				
				$
				2,384
		﻿
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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
				
				March 31,﻿
				
				2019
				
				2018﻿Stock-based compensation within operations and maintenance expenses
				
				$
				997
				
				$
				859﻿Income tax benefit
				
				
				227
				
				
				241
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|﻿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
				
				March 31,﻿
				
				2019
				
				2018﻿Stock-based compensation within operations and maintenance expenses
				
				$
				425
				
				$
				351﻿Income tax benefit
				
				
				120
				
				
				100
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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
				
				March 31,﻿
				
				2019
				
				2018﻿Stock-based compensation within operations and maintenance expenses
				
				$
				328
				
				$
				94﻿Income tax benefit
				
				
				92
				
				
				58﻿
		﻿                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
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|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|﻿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
				
				March 31,﻿
				
				2019
				
				2018﻿Stock-based compensation within operations and maintenance expenses
				
				$
				180
				
				$
				140﻿Income tax benefit
				
				
				52
				
				
				40
		﻿                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
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|﻿                                                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|﻿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
				
				4,904
				
				
				36.73﻿Vested
				
				(4,904)
				
				
				36.73﻿Nonvested 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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