Income Tax (details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Components of Deferred Tax Assets and Liabilities [Abstract]
Deferred Tax Liabilities, Property, Plant and Equipment	$ 322,527,000								$ 362,160,000	$ 322,527,000
Deferred Tax Liabilities, Regulatory Assets	60,253,000								56,183,000	60,253,000
Deferred Tax Liabilities, Regulatory Assets and Liabilities	49,197,000								71,971,000	49,197,000
Deferred Tax Liabilities Non Regulated Liabilities	43,824,000								47,516,000	43,824,000
Deferred Tax Liabilities, Net	475,801,000								537,830,000	475,801,000
Deferred Tax Assets, Regulatory Assets and Liabilities	(7,724,000)								0	(7,724,000)
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits	6,024,000								4,112,000	6,024,000
Deferred Tax Assets Non Regulated Assets	(1,235,000)								0	(1,235,000)
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	1,986,000								1,939,000	1,986,000
Deferred Tax Assets, Tax Credit Carryforwards, Other	32,997,000								45,351,000	32,997,000
Deferred Tax Assets, Net	32,048,000								51,402,000	32,048,000
Deferred Tax Assets (Liabilities), Net	443,753,000								486,428,000	443,753,000
Accumulated Deferred Investment Tax Credit	624,000								367,000	624,000
Deferred Tax Liabilities, Other	444,377,000								486,795,000	444,377,000
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate									35,785,000	35,764,000	37,056,000
Income Tax Reconciliation, State and Local Income Taxes									4,674,000	4,773,000	4,945,000
Income Tax Reconciliation, Tax Credits, Investment									(271,000)	(350,000)	(442,000)
Differences Regulatory Commission									2,357,000	1,718,000	1,647,000
Income Tax Reconciliation, Tax Credits, Other									(864,000)	(800,000)	(786,000)
One-Time Tax Adjustment, Net of Federal Benefit	2,700,000				0				0	2,700,000	0
Income Tax Reconciliation, Other Adjustments									24,000	(402,000)	405,000
Income Tax Expense (Benefit)	18,217,000	(3,245,000)	768,000	27,663,000	19,600,000	(5,840,000)	1,181,000	27,884,000	41,705,000	43,403,000	42,825,000
Effective Income Tax Rate									40.80%	42.50%	40.50%
Income Tax Disclosure [Abstract]
Federal Operating Loss Carryfoward									113,000,000
State Operating Loss Carryforward									113,700,000
IRS Tax Payment Due To Examination										200,000
Tax Provision Current And Deferred [Abstract]
Current Federal Tax Expense (Benefit)									(62,000)	1,693,000	130,000
Current State and Local Tax Expense (Benefit)									(11,000)	99,000	(929,000)
Current Income Tax Expense (Benefit)									(73,000)	1,792,000	(799,000)
Deferred Federal Income Tax Expense (Benefit)									35,109,000	31,187,000	35,021,000
Deferred State and Local Income Tax Expense (Benefit)									6,669,000	10,424,000	8,603,000
Deferred Income Tax Expense (Benefit)									41,778,000	41,611,000	43,624,000
Income Tax Expense (Benefit)	18,217,000	(3,245,000)	768,000	27,663,000	19,600,000	(5,840,000)	1,181,000	27,884,000	41,705,000	43,403,000	42,825,000
Income Taxes Paid									870,000	2,979,000	1,756,000
Tax Provision Regulated And Nonutility [Abstract]
Regulated Current Tax Expense Benefit									(73,000)	1,909,000	(4,646,000)
Regulated Deferred And Local Tax Expense Benefit									38,073,000	39,163,000	49,595,000
Regulated Investments And Credits Tax Expense Benefit									(271,000)	(350,000)	(422,000)
Total Tax Provision Related To Regulated Utility									37,729,000	40,722,000	44,527,000
Non Utility Current Tax Expense Benefit									0	(117,000)	3,846,000
Non Utility Deferred And Local Tax Expense Benefit									3,976,000	2,798,000	(5,548,000)
Total Tax Provision Related To Non Utility									3,976,000	2,681,000	(1,702,000)
Income Tax Expense (Benefit)	$ 18,217,000	$ (3,245,000)	$ 768,000	$ 27,663,000	$ 19,600,000	$ (5,840,000)	$ 1,181,000	$ 27,884,000	$ 41,705,000	$ 43,403,000	$ 42,825,000