Changes in Accumulated Other Comprehensive Loss by Component - Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Amounts reclassified from accumulated other comprehensive loss:
Interest expense, net									$ 16,782	$ 16,943	$ 18,336
Tax expense (benefit)									13,451	11,854	(2,409)
Reclassification net of tax	$ (11,560)	$ (12,429)	$ (25,474)	$ 297	$ (14,696)	$ (9,921)	$ (21,164)	$ 1,876	(48,527)	(43,321)	$ (54,609)
Other Postretirement Benefit Liability | Amount reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive loss:
Actuarial (gains) losses									(312)	(211)
Tax expense (benefit)									78	53
Reclassification net of tax									(234)	(158)
Pension Liability | Amount reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive loss:
Actuarial (gains) losses									595	706
Tax expense (benefit)									(149)	(177)
Reclassification net of tax									446	529
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									499	(328)
Tax expense (benefit)									(125)	82
Reclassification net of tax									$ 374	$ (246)