Long-term Debt - Debt Summary (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Long-term Debt
Long-term debt	$ 1,688,149	$ 1,735,198
Less current maturities of long-term debt	(100,664)	(92,108)
Less net discounts	(653)	(686)
Less debt issuance costs, net of accumulated amortization of $16.9 million and $13.3 million, respectively	(19,679)	(23,553)
Long-term debt, net of current maturities and debt issuance costs	1,567,153	1,618,851
Accumulated amortization for debt issuance costs	16,900	13,300
Senior Secured Credit Facility
Long-term Debt
Long-term debt	1,220,792	1,259,740
$300 million 5.875% senior unsecured notes due November 1, 2021
Long-term Debt
Long-term debt	$ 300,000	$ 300,000
Interest rate (as a percent)	5.875%	5.875%
Principal amount	$ 300,000
Other long-term obligations
Long-term Debt
Long-term debt	139,759	$ 146,992
Capital leases
Long-term Debt
Long-term debt	$ 27,598	$ 28,466