Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ (182,700)	$ (155,431)	$ (190,435)	$ (152,193)
Other comprehensive income (loss) before reclassifications	46	1,644	4,909	(4,492)
Amounts reclassified from accumulated other comprehensive income (net of tax)	2,662	3,011	5,534	5,909
Net current-period other comprehensive income (loss)	2,708	4,655	10,443	1,417
Ending balance	(179,992)	(150,776)	(179,992)	(150,776)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Tax	(1,696)	(1,918)	(3,524)	(3,763)
Foreign Currency
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(7,553)	(5,852)	(12,416)	284
Other comprehensive income (loss) before reclassifications	46	1,644	4,909	(4,492)
Amounts reclassified from accumulated other comprehensive income (net of tax)	0	0	0	0
Net current-period other comprehensive income (loss)	46	1,644	4,909	(4,492)
Ending balance	(7,507)	(4,208)	(7,507)	(4,208)
Pension and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(175,147)	(149,579)	(178,019)	(152,477)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income (net of tax)	2,662	3,011	5,534	5,909
Net current-period other comprehensive income (loss)	2,662	3,011	5,534	5,909
Ending balance	$ (172,485)	$ (146,568)	$ (172,485)	$ (146,568)