Long-term Debt - Debt Summary (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017	Jan. 19, 2017
Long-term Debt
Long-term debt	$ 1,227,123,000	$ 1,280,201,000
Less current maturities of long-term debt	(35,498,000)	(35,612,000)
Less discount on senior secured credit facility Term Loan B	(2,251,000)	(2,558,000)
Less debt issuance costs	(25,227,000)	(27,406,000)
Long-term debt, net of current maturities and debt issuance costs	1,164,147,000	1,214,625,000
Senior Secured Credit Facility
Long-term Debt
Long-term debt	715,000,000	760,000,000
Senior Unsecured Notes 5.625 Percent Due January 15, 2027
Long-term Debt
Long-term debt	400,000,000	400,000,000
Principal amount	$ 400,000,000		$ 400,000,000
Interest rate (as a percent)	5.625%		5.625%
Other long-term obligations
Long-term Debt
Long-term debt	$ 111,674,000	119,310,000
Capital leases
Long-term Debt
Long-term debt	$ 449,000	$ 891,000