|**Stock-Based Compensation (Tables)**                                              | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
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|**Share-based Compensation Arrangement by Share-based Payment Award [Line Items]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Summary Of Nonvested PSU Transactions                                              | Number
				
				Weightedof
				
				AverageShare Units
				
				Fair ValueNonvested share units at beginning of period
				
				
				528,092
				
				$
				21.25Granted
				
				
				143,630
				
				
				25.31Performance criteria adjustment
				
				
				16,927
				
				
				19.45Forfeited
				
				
				(3,939)
				
				
				22.23Share units vested in prior period and issued in current period
				
				
				18,000
				
				
				19.51Share units issued
				
				
				(174,148)
				
				
				18.93Nonvested share units at end of period
				
				
				528,562
				
				$
				22.99
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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 Nonvested RSU Transactions                                              | Number
				
				Weightedof
				
				AverageStock Units
				
				Fair ValueNonvested stock units at beginning of period
				
				
				112,666
				
				$
				20.16Granted
				
				
				41,150
				
				
				24.80Stock units vested but not paid
				
				
				(5,750)
				
				
				17.99Stock units vested and paid
				
				
				(24,772)
				
				
				17.77Forfeited
				
				
				-
				
				
				-Nonvested stock units at end of period
				
				
				123,294
				
				$
				22.29                                                                                                          
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|                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                                                   | Nonvested stock units at beginning of period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|                                                                                   | Granted                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|                                                                                   | Stock units vested but not paid                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                                                   | Stock units vested and paid                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|                                                                                   | Forfeited                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|                                                                                   | Nonvested stock units at end of period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Summary Of Stock Option Transactions                                               | Weighted
				
				WeightedAverage
				
				Average
				
				AggregateExercise
				
				Remaining
				
				IntrinsicShares
				
				Price
				
				Life (years)
				
				ValueOutstanding at beginning of period
				
				1,538,110
				
				$
				16.82Forfeited
				
				-
				
				
				-Expired
				
				(2,707)
				
				
				17.98Exercised
				
				(188,736)
				
				
				14.61Outstanding and exercisable at end of period
				
				1,346,667
				
				$
				17.13
				
				3.7
				
				$
				10,692                                                                                      
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|                                                                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                                                   | Outstanding at beginning of period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|                                                                                   | Forfeited                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|                                                                                   | Expired                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|                                                                                   | Exercised                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|                                                                                   | Outstanding and exercisable at end of period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Summary Of Nonvested Share Activity - Restricted Stock                             | Number
				
				Weightedof
				
				AverageShares
				
				Fair ValueNonvested shares at beginning of period
				
				
				62,500
				
				$
				17.70Granted
				
				
				-
				
				
				-Vested
				
				
				(31,250)
				
				
				17.70Forfeited
				
				
				-
				
				
				-Nonvested shares at end of period
				
				
				31,250
				
				$
				17.70                                                                                                                                                                                                                                  
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|                                                                                   | Nonvested shares at beginning of period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|                                                                                   | Granted                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|                                                                                   | Vested                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|                                                                                   | Forfeited                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|                                                                                   | Nonvested shares 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 EndedMarch 31,2014
				
				2013Stock-based compensation for performance share units within operations and maintenance expenses
				
				$
				1,002
				
				$
				715Income tax benefit
				
				
				410
				
				
				291                                                                                                                                                                                                                                                                                                                                                          
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|                                                                                   | Stock-based compensation for performance share units 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 EndedMarch 31,2014
				
				2013Stock-based compensation for restricted stock units within operations and maintenance expenses
				
				$
				236
				
				$
				178Income tax benefit
				
				
				98
				
				
				73                                                                                                                                                                                                                                                                                                                                                               
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|                                                                                   | Stock-based compensation for restricted stock units 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 EndedMarch 31,2014
				
				2013Stock-based compensation for stock options within operations and maintenance expenses
				
				$
				-
				
				$
				30Income tax benefit
				
				
				73
				
				
				238                                                                                                                                                                                                                                                                                                                                                                          
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|                                                                                   | Stock-based compensation for stock options within operations and maintenance expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|                                                                                   | Income tax benefit                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
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|Restricted Stock [Member]                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|**Share-based Compensation Arrangement by Share-based Payment Award [Line Items]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Summary Of Compensation Costs                                                      | Three Months EndedMarch 31,2014
				
				2013Stock-based compensation for restricted stock within operations and maintenance expenses
				
				$
				92
				
				$
				92Income tax benefit
				
				
				38
				
				
				38                                                                                                                                                                                                                                                                                                                                                                       
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|                                                                                   | Stock-based compensation for restricted stock within operations and maintenance expenses                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|                                                                                   | Income tax benefit                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
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