CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 17,647	$ 33,371	$ 7,888	$ 72,572
Other comprehensive income (loss):
Cumulative translation adjustments	0	(1,208)	0	(1,055)
Pension and other postretirement liability adjustment, net of tax	1,632	1,550	3,276	3,035
Other comprehensive income	1,632	342	3,276	1,980
Comprehensive income	$ 19,279	$ 33,713	$ 11,164	$ 74,552