Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ (187,533)	$ (179,992)	$ (196,600)	$ (190,435)
Other comprehensive income (loss) before reclassifications	3,527	(1,106)	6,322	3,803
Amounts reclassified from accumulated other comprehensive income (net of tax)	3,136	2,767	9,408	8,301
Net current-period other comprehensive income (loss)	6,663	1,661	15,730	12,104
Ending balance	(180,870)	(178,331)	(180,870)	(178,331)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Tax	(1,997)	(1,762)	(5,990)	(5,286)
Foreign Currency
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(7,548)	(7,507)	(10,343)	(12,416)
Other comprehensive income (loss) before reclassifications	3,527	(1,106)	6,322	3,803
Amounts reclassified from accumulated other comprehensive income (net of tax)	0	0	0	0
Net current-period other comprehensive income (loss)	3,527	(1,106)	6,322	3,803
Ending balance	(4,021)	(8,613)	(4,021)	(8,613)
Pension and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(179,985)	(172,485)	(186,257)	(178,019)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income (net of tax)	3,136	2,767	9,408	8,301
Net current-period other comprehensive income (loss)	3,136	2,767	9,408	8,301
Ending balance	$ (176,849)	$ (169,718)	$ (176,849)	$ (169,718)