Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income (loss)	$ (191,467)	$ 106,769	$ (266,090)	$ 242,350
Derivative instruments
Comprehensive income (loss) before tax	476	(2,360)	(1,830)	(2,421)
Other comprehensive income (loss), derivative instruments, net of tax	476	(2,360)	(1,830)	(2,421)
Pension, postretirement and other post-employment benefits
Comprehensive income (loss) before tax	4,164	(4,019)	(12,439)	(1,117)
Other comprehensive income (loss), pension, postretirement and other post-employment benefits, net of tax	4,164	(4,019)	(12,439)	(1,117)
Available-for-sale securities
Comprehensive income (loss) before tax	(255)	(98)	(189)	553
Other comprehensive income (loss), available-for-sale securities, net of tax	(255)	(98)	(189)	553
Total other comprehensive income (loss)	4,385	(6,477)	(14,458)	(2,985)
Total comprehensive income (loss)	$ (187,082)	$ 100,292	$ (280,548)	$ 239,365