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 (loss)	$ (79,760)	$ 98,620	$ 83,300
Other comprehensive income
Defined benefit plans	1,310	(1,470)	3,250
Foreign currency translation	6,880	10,290	(6,880)
Derivative instruments	(7,810)	3,300	4,110
Total other comprehensive income	380	12,120	480
Total comprehensive income (loss)	$ (79,380)	$ 110,740	$ 83,780