CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income		$ 200,529	$ 681,070	$ 557,043
Postretirement benefits:
Net actuarial gain (loss)	[1]	1,634	(2,530)	2,461
Amortization of prior service cost	[2]	(547)	(547)	(547)
Amortization of net loss	[3]	(28)	0	0
Cumulative effect of adoption of ASU 2018-02 reclassified to retained earnings		0	0	446
Total other comprehensive income		1,059	(3,077)	2,360
Comprehensive income		$ 201,588	$ 677,993	$ 559,403

[1] Net of income taxes of $(484), $749 and $(704) for the year ended December 31, 2020, 2019 and 2018, respectively.

[2] Net of income taxes of $162, $162 and $162 for the year ended December 31, 2020, 2019 and 2018, respectively.

[3] Net of income taxes of $8 for the year ended December 31, 2020.