Consolidated Statements of Comprehensive (Loss) Income - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (18,701)	$ 8,035	$ (734)	$ 456	$ 2,277	$ 4,613	$ 6,129	$ 93,344	$ (10,944)	$ 106,363	$ 25,170
Other comprehensive (loss) income, net of tax:
Changes in pension liabilities and other post-retirement benefit obligations									(8,490)	(35,521)	(83,887)
Tax effect of changes in pension liabilities and other post-retirement benefit obligations									3,107	13,571	31,924
Foreign currency translation adjustments									(2,119)	(1,855)	(1,928)
Tax effect of changes in foreign currency translation adjustments									(113)	235	0
Other comprehensive loss									(7,615)	(23,570)	(53,891)
Comprehensive (loss) income	$ (26,122)	$ 7,791	$ (813)	$ 585	$ (21,668)	$ 4,411	$ 6,476	$ 93,574	$ (18,559)	$ 82,793	$ (28,721)