Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ (250,154)	$ (196,600)
Other comprehensive (loss) income before reclassifications	(2,476)	591
Amounts reclassified from accumulated other comprehensive income (net of tax)	4,845	3,101
Net current-period other comprehensive (loss) income	2,369	3,692
Ending balance	(247,785)	(192,908)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	(1,680)	(1,974)
Foreign Currency
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(4,602)	(10,343)
Other comprehensive (loss) income before reclassifications	(2,476)	591
Amounts reclassified from accumulated other comprehensive income (net of tax)	0	0
Net current-period other comprehensive (loss) income	(2,476)	591
Ending balance	(7,078)	(9,752)
Pension and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(245,552)	(186,257)
Other comprehensive (loss) income before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income (net of tax)	4,845	3,101
Net current-period other comprehensive (loss) income	4,845	3,101
Ending balance	$ (240,707)	$ (183,156)