Changes in Accumulated Other Comprehensive Loss by Component - Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amounts reclassified from accumulated other comprehensive loss:
Interest expense, net									$ 16,943	$ 18,336	$ 15,195
Tax expense (benefit)									11,854	(2,409)	24,687
Reclassification net of tax	$ (14,696)	$ (9,921)	$ (21,164)	$ 1,876	$ (34,528)	$ (9,327)	$ (14,746)	$ 3,277	(43,321)	(54,609)	$ (38,469)
Other Postretirement Benefit Liability | Amount reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive loss:
Actuarial (gains) losses									(211)	(107)
Tax expense (benefit)									53	41
Reclassification net of tax									(158)	(66)
Pension Liability | Amount reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive loss:
Actuarial (gains) losses									706	723
Tax expense (benefit)									(177)	(275)
Reclassification net of tax									529	448
Unrealized Net Loss on Interest Rate Swap | Interest rate swap | Amount reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive loss:
Interest expense, net									(328)	330
Tax expense (benefit)									82	(125)
Reclassification net of tax									$ (246)	$ 205