CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Parent [Line Items]
Net income (loss)	$ (12,958)	$ 8,540	$ 135,747	$ 176,919
Other comprehensive income (loss):
Net unrealized gain (loss) from pension and postretirement plans, net of tax	(314)	393	(1,306)	(367)
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax	0	0	347	(107)
Other Comprehensive Income Reclassification Of Net Unrealized Gain Loss On Interest Rate Swaps During Period Net Of Tax	0	811	94	2,526
Other comprehensive income (loss)	(314)	1,204	(865)	2,052
Comprehensive income (loss)	(13,272)	9,744	134,882	178,971
Subsidiaries [Member]
Parent [Line Items]
Net income (loss)	3,057	26,605	181,973	233,205
Other comprehensive income (loss):
Net unrealized gain (loss) from pension and postretirement plans, net of tax	1,880	3,406	5,305	8,671
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax	0	0	718	1,811
Amortization Of Financing Cash Flow Hedge Contracts To Earnings During Period Net Of Tax	79	79	237	237
Other comprehensive income (loss)	1,959	3,485	6,260	10,719
Comprehensive income (loss)	5,016	30,090	188,233	243,924
Reclassification out of Accumulated Other Comprehensive Income [Member] | Parent Company [Member]
Other comprehensive income (loss):
Comprehensive income (loss)	314	(1,204)	(80)	(4,433)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Subsidiaries [Member]
Other comprehensive income (loss):
Comprehensive income (loss)	(1,959)	(3,485)	(7,205)	(13,100)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net unrealized gain (loss) and prior service cost on pension plans | Parent Company [Member]
Parent [Line Items]
Net income (loss)	314	(393)	361	(2,014)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net unrealized gain (loss) and prior service cost on pension plans | Subsidiaries [Member]
Parent [Line Items]
Net income (loss)	$ (1,880)	$ (3,406)	$ (6,250)	$ (11,051)