Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income (loss)	$ (49,324)	$ 62,840	$ (74,623)	$ 135,581
Derivative instruments
Comprehensive income (loss) before tax	363	(2,778)	(2,306)	(61)
Other comprehensive income (loss), derivative instruments, net of tax	363	(2,778)	(2,306)	(61)
Pension, postretirement and other post-employment benefits
Comprehensive income (loss) before tax	(2,336)	2,902	(16,603)	2,902
Other comprehensive income (loss), pension, postretirement and other post-employment benefits, net of tax	(2,336)	2,902	(16,603)	2,902
Available-for-sale securities
Comprehensive income (loss) before tax	533	274	66	651
Other comprehensive income (loss), available-for-sale securities, net of tax	533	274	66	651
Total other comprehensive income (loss)	(1,440)	398	(18,843)	3,492
Total comprehensive income (loss)	$ (50,764)	$ 63,238	$ (93,466)	$ 139,073