CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Parent [Line Items]
Net income (loss)	$ 25,616	$ 41,113	$ 141,292	$ 148,705
Other comprehensive income (loss):
Net unrealized gain (loss) from pension and postretirement plans, net of tax	1,277	(783)	1,856	(992)
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax	0	0	333	347
Other Comprehensive Income Reclassification Of Net Unrealized Gain Loss On Interest Rate Swaps During Period Net Of Tax	0	0	0	94
Other comprehensive income (loss)	1,277	(783)	2,189	(551)
Comprehensive income (loss)	26,893	40,330	143,481	148,154
Subsidiaries [Member]
Parent [Line Items]
Net income (loss)	42,699	57,834	171,799	178,916
Other comprehensive income (loss):
Net unrealized gain (loss) from pension and postretirement plans, net of tax	4,094	1,424	7,475	3,425
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax	0	0	686	718
Amortization Of Financing Cash Flow Hedge Contracts To Earnings During Period Net Of Tax	79	79	158	158
Other comprehensive income (loss)	4,173	1,503	8,319	4,301
Comprehensive income (loss)	$ 46,872	$ 59,337	$ 180,118	$ 183,217