Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ (192,908)	$ (182,700)	$ (196,600)	$ (190,435)
Other comprehensive income (loss) before reclassifications	2,204	46	2,795	4,909
Amounts reclassified from accumulated other comprehensive income (net of tax)	3,171	2,662	6,272	5,534
Net current-period other comprehensive income (loss)	5,375	2,708	9,067	10,443
Ending balance	(187,533)	(179,992)	(187,533)	(179,992)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Tax	(2,019)	(1,696)	(3,993)	(3,524)
Foreign Currency
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(9,752)	(7,553)	(10,343)	(12,416)
Other comprehensive income (loss) before reclassifications	2,204	46	2,795	4,909
Amounts reclassified from accumulated other comprehensive income (net of tax)	0	0	0	0
Net current-period other comprehensive income (loss)	2,204	46	2,795	4,909
Ending balance	(7,548)	(7,507)	(7,548)	(7,507)
Pension and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(183,156)	(175,147)	(186,257)	(178,019)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income (net of tax)	3,171	2,662	6,272	5,534
Net current-period other comprehensive income (loss)	3,171	2,662	6,272	5,534
Ending balance	$ (179,985)	$ (172,485)	$ (179,985)	$ (172,485)