Stock-Based Compensation (details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
ESPP Paragraph [Abstract]
Percent Of Offering Date Price Employees Are Allowed To Purchase Stock	85.00%
Maximum Value Of Stock Employees Are Allowed To Purchase	$ 21,236
LTIP Paragraph 1 [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	850,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	241,169
Additional Ltip Shares Authorized	250,000
LTIP Paragraph 2 [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 43.39	$ 51.42
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 30.86
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 38.96
Unrecognized compensation cost	1,600,000
LTIP Table 1 [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	9,516	9,924	8,428
Allocated Share-based Compensation Expense	400,000	500,000	400,000
Cumulative LTIP Expense Evaluation Period Vesting In Current Year	960,000
Cumulative LTIP Expense Evaluation Period Vested In Prior Year	1,200,000
Cumulative LTIP Expense Evaluation Period Vested Two Years Ago	800,000
LTIP Table 2 [Abstract]
Target LTIP Award For Period Vesting In Current Year	37,950,000
Target LTIP Award For Period Vesting Next Year	35,340,000
Target LTIP Award For Period Vesting In Two Years	37,300,000
Target LTIP Award For All Periods	110,590,000
Maximum LTIP Award For Period Vesting In Current Year	75,900,000
Maximum LTIP Award For Period Vesting Next Year	70,680,000
Maximum LTIP Award For Period Vesting In Two Years	74,600,000
Maximum LTIP Award For All Periods	221,180,000
Current Year Expense LTIP Award For Period Vesting In Current Year	390,000
Current Year Expense LTIP Award For Period Vesting Next Year	603,000
Current Year Expense LTIP Award For Period Vesting In Two Years	486,000
Current Year Expense LTIP Award For All Periods	1,479,000
Cumulative LTIP Expense Evaluation Period Vesting In Current Year	960,000
Cumulative Expense LTIP Award For Period Vesting Next Year	1,238,000
Cumulative Expense LTIP Award For Period Vesting In Two Years	486,000
RSU Paragraph 1 [Abstract]
Employee Service Share-based Compensation, Nonvested Restricted Stock Unit Awards, Compensation Cost Not yet Recognized	1,500,000
Unrecognized compensation cost, restricted stock units, period for recognition	through 2017
RSU Table 1 [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	44,567	24,864	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	25,748	25,224
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	(5,455)	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(590)	(360)
Share-based Compensation Arrangement by Share-based Payment Award, Restricted Stock Units, Nonvested, Weighted Average Grant Date Fair Value	$ 46.27	$ 47.57	$ 0.00
Share-based Compensation Arrangement by Share-based Payment Award, Restricted Stock Units, Grants in Period, Weighted Average Grant Date Fair Value	$ 45.38	$ 47.58
Share-based Compensation Arrangement by Share-based Payment Award, Restricted Stock Units, Vested in Period, Weighted Average Grant Date Fair Value	$ 48.01	$ 0.00
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 46.58	$ 48.00
SOP Paragraph 1 [Abstract]
Reserved Shares Stock Options	492,150	529,925	579,225	490,460
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	10 years 7 days
Option Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Method Used	Black-Scholes
SOP Paragraph 2 [Abstract]
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options	1,100,000
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	(242,000)	(149,000)	(26,000)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	500,000	600,000	600,000
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Remaining Contractual Term	4 years 9 months 17 days
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Remaining Contractual Term	5 years 1 month 5 days
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options	200,000
Unrecognized compensation cost, period for recognition	during 2014
SOP Table 1 [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate			2.00%
Option Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Term			4.5
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate			24.50%
Option Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate			3.80%
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Forfeiture Rate			3.10%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value			$ 6.73
SOP Table 2 [Abstract]
Reserved Shares Stock Options	492,150	529,925	579,225	490,460
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross			122,700
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(33,800)	(46,825)	(24,185)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period	(3,975)	(2,475)	(9,750)
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options	409,036
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Exercise Price	$ 42.89	$ 42.22	$ 42.09	$ 40.82
Stock Price On Stock Option Plan Grant Date			$ 45.74
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	$ 32.16	$ 40.62	$ 33.88
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	$ 43.72	$ 43.78	$ 44.38
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	300,000	400,000	300,000
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price	$ 42.41
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	600,000	1,300,000	3,400,000	2,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	600,000
Stock Based Compensation FS Impact Summary Table [Abstract]
Stock Based Compensation Charged To Operations And Maintenance	1,876,000	1,668,000	1,477,000
Income Tax Benefit Of Stock Based Compensation	(765,000)	(707,000)	(597,000)
Net Income Impact Of Stock Based Compensation	1,111,000	961,000	880,000
Stock Based Compensation Capitalized	$ 331,000	$ 294,000	$ 261,000