CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income		$ 681,070	$ 557,043	$ 100,393
Postretirement benefits:
Net actuarial gain (loss)	[1]	(2,530)	2,461	(2,634)
Prior service credit	[2]	0	0	5,449
Amortization of prior service cost	[3]	(547)	(547)	(1,723)
Cumulative effect of adoption of ASU 2018-02 reclassified to retained earnings		0	446	0
Total other comprehensive income		(3,077)	2,360	1,092
Comprehensive income		$ 677,993	$ 559,403	$ 101,485

[1] Net of income taxes of $749, $(704) and $1,544 for the year ended December 31, 2019, 2018 and 2017, respectively.

[2] Net of income taxes of $0, $0 and $(3,194) for the year ended December 31, 2019, 2018 and 2017, respectively.

[3] Net of income taxes of $162, $162 and $1,010 for the year ended December 31, 2019, 2018 and 2017, respectively.