Net Investment in Finance Leases Net Investment in Finance Leases (Details) $ in Thousands	Sep. 30, 2017 USD ($) Aircraft	Dec. 31, 2016 USD ($)
Capital Leased Assets, Number of Units | Aircraft	28
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Total lease payments to be received	$ 297,061
Less: Unearned income	(153,253)
Estimated residual values of leased flight equipment (unguaranteed)	344,600
Net investment in finance and sales-type leases	488,408	$ 260,853
Receivable in Remainder of Fiscal Year	14,948
Receivable in Year Two	54,842
Receivable in Year Three	54,507
Receivable in Year Four	52,287
Receivable in Year Five	42,691
Thereafter	77,786
Total	$ 297,061