Net Investment in Finance Leases Net Investment in Finance Leases (Details) $ in Thousands	Jun. 30, 2017 USD ($) Aircraft	Dec. 31, 2016 USD ($)
Capital Leased Assets, Number of Units | Aircraft	21
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Total lease payments to be received	$ 224,360
Less: Unearned income	(110,486)
Estimated residual values of leased flight equipment (unguaranteed)	240,600
Net investment in finance and sales-type leases	354,474	$ 260,853
Receivable in Remainder of Fiscal Year	22,004
Receivable in Year Two	38,042
Receivable in Year Three	37,707
Receivable in Year Four	37,287
Receivable in Year Five	30,931
Thereafter	58,389
Total	$ 224,360