CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Net Income (Loss) Attributable to Parent	$ 55,242	$ (23,233)	$ 244,235	$ 71,703
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Net unrealized gain (loss) from pension and postretirement plans, net of tax	2,386	1,630	4,771	6,800
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent, Total	2,386	1,630	4,771	6,800
Comprehensive Income (Loss), Net of Tax, Attributable to Parent, Total	57,628	(21,603)	249,006	78,503
Subsidiaries [Member]
Net Income (Loss) Attributable to Parent	78,364	15,037	277,834	126,358
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Net unrealized gain (loss) from pension and postretirement plans, net of tax	4,459	3,860	8,917	11,570
Amortization Of Financing Cash Flow Hedge Contracts To Earnings During Period Net Of Tax	96	96	192	192
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent, Total	4,555	3,956	9,109	11,762
Comprehensive Income (Loss), Net of Tax, Attributable to Parent, Total	$ 82,919	$ 18,993	$ 286,943	$ 138,120