Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Consolidated Statements of Comprehensive Income (Loss)
Net income (loss)	$ 337,573	$ (344,615)	$ 233,799
Derivative instruments
Comprehensive income (loss) before tax	2,128	(1,328)	(5,892)
Other comprehensive income (loss), derivative instruments, net of tax	2,128	(1,328)	(5,892)
Pension, postretirement and other post-employment benefits
Comprehensive income (loss) before tax	47,562	(39,732)	(32,038)
Other comprehensive income (loss), pension, postretirement and other post-employment benefits, net of tax	47,562	(39,732)	(32,038)
Available-for-sale securities
Comprehensive income (loss) before tax	169	(330)	323
Other comprehensive income (loss), available-for-sale securities, net of tax	169	(330)	323
Total other comprehensive income (loss)	49,859	(41,390)	(37,607)
Total comprehensive income (loss)	$ 387,432	$ (386,005)	$ 196,192