CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Parent [Line Items]
Net income (loss)	$ 41,113	$ 905	$ 148,705	$ 168,380
Other comprehensive income (loss):
Net unrealized gain (loss) from pension and postretirement plans, net of tax	(783)	(1,107)	(992)	(760)
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	861	94	1,715
Other comprehensive income (loss)	(783)	(246)	(551)	848
Comprehensive income (loss)	40,330	659	148,154	169,228
Subsidiaries [Member]
Parent [Line Items]
Net income (loss)	57,834	26,663	178,916	206,601
Other comprehensive income (loss):
Net unrealized gain (loss) from pension and postretirement plans, net of tax	1,424	1,879	3,425	5,265
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	158	158
Other comprehensive income (loss)	1,503	1,958	4,301	7,234
Comprehensive income (loss)	$ 59,337	$ 28,621	$ 183,217	$ 213,835