Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income (loss)	$ (25,299)	$ 72,741
Derivative instruments
Comprehensive income (loss) before tax	(2,669)	2,717
Other comprehensive income (loss), derivative instruments, net of tax	(2,669)	2,717
Pension, postretirement and other post-employment benefits
Comprehensive income (loss) before tax	(14,267)
Other comprehensive income (loss), pension, postretirement and other post-employment benefits, net of tax	(14,267)
Available-for-sale securities
Comprehensive income (loss) before tax	(467)	377
Other comprehensive income (loss), available-for-sale securities, net of tax	(467)	377
Total other comprehensive income (loss)	(17,403)	3,094
Total comprehensive income (loss)	$ (42,702)	$ 75,835