Debt and Other Obligations - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Amortization of deferred financing costs	$ 2,175	$ 1,784	$ 6,544	$ 4,930
Interest Expense, Other	281	49	400	182
Total	25,138	21,925	75,375	60,272
Senior Loans [Member]
Debt Instrument [Line Items]
Interest expense, term loans	3,809	4,195	11,632	12,769
Junior Loans [Member]
Debt Instrument [Line Items]
Interest expense, term loans	454	605	1,467	1,908
Fixed Rate Loan [Member]
Debt Instrument [Line Items]
Interest expense, term loans	6,517	4,844	19,151	14,636
Equipment Notes, Series A 2015-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	3,747	4,057	11,294	12,214
Equipment Notes, Series B 2015-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	850	939	2,570	2,881
Equipment Notes, Series C 2015-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	1,279	1,420	3,894	2,209
Equipment Notes, Series AA 2017-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	1,973	1,751	5,959	4,008
Equipment Notes, Series A 2017-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	711	631	2,148	1,445
Equipment Notes, Series B 2017-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	708	700	2,199	1,636
Equipment Notes, Series C 2017-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	1,104	934	3,275	1,400
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Interest expense, term loans	1,493	0	4,466	0
Finance Lease Obligations [Member]
Debt Instrument [Line Items]
Interest expense, term loans	$ 37	$ 16	$ 376	$ 54