CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Net Income (Loss) Attributable to Parent	$ 188,993	$ 94,936
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Net unrealized gain (loss) from pension and postretirement plans, net of tax	2,385	5,170
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent, Total	2,385	5,170
Comprehensive Income (Loss), Net of Tax, Attributable to Parent, Total	191,378	100,106
Subsidiaries [Member]
Net Income (Loss) Attributable to Parent	199,470	111,321
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Net unrealized gain (loss) from pension and postretirement plans, net of tax	4,458	7,710
Amortization Of Financing Cash Flow Hedge Contracts To Earnings During Period Net Of Tax	96	96
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent, Total	4,554	7,806
Comprehensive Income (Loss), Net of Tax, Attributable to Parent, Total	$ 204,024	$ 119,127