Debt and Other Obligations - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Debt Instrument [Line Items]
Commitment fees	$ 52	$ 30
Amortization of debt discounts	1,491	1,231
Total	17,803	12,388
Senior Loans [Member]
Debt Instrument [Line Items]
Interest expense, term loans	4,317	4,672
Junior Loans [Member]
Debt Instrument [Line Items]
Interest expense, term loans	667	803
Fixed Rate Loan [Member]
Debt Instrument [Line Items]
Interest expense, term loans	4,911	159
Equipment Notes, Series A 2015-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	4,142	4,308
Equipment Notes, Series B 2015-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	1,012	1,185
Equipment Notes, Series AA 2017-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	682	0
Equipment Notes, Series A 2017-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	246	0
Equipment Notes, Series B 2017-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	$ 283	$ 0