Debt and Other Obligations - Long-term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term debt, gross	$ 659,300	$ 148,000
Less current maturities	49,637	10,431
Less unamortized discount, net	13,000	2,400
Total	596,693	135,232
Senior loans
Debt Instrument [Line Items]
Long-term debt, gross	$ 484,200	$ 132,000
Weighted-average interest rates	4.10%	4.26%
Junior loans
Debt Instrument [Line Items]
Long-term debt, gross	$ 54,300	$ 16,000
Weighted-average interest rates	6.90%	6.94%
Equipment Notes, Series A [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 95,800	$ 0
Weighted-average interest rates	4.03%
Equipment Notes, Series B [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 25,000	$ 0
Weighted-average interest rates	4.37%