Fair Value Measurements - Nonrecurring Basis (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) engine aircraft	Sep. 30, 2017 USD ($) engine aircraft	Sep. 30, 2018 USD ($) engine aircraft	Sep. 30, 2017 USD ($) engine aircraft	Dec. 31, 2017 USD ($)
Assets at fair value and gains (losses) recorded
Equipment held for sale	$ 40,931		$ 40,931		$ 34,172
Assets at fair value	$ 2,800		2,800		1,100
Increase (decrease) in asset write-down			$ 4,800
Number of engines | engine	4	7	4	7
Number of aircraft | aircraft	6	3	6	3
Asset write-down	$ 1,215	$ 6,226	$ 4,793	$ 19,668
Engine and aircraft
Assets at fair value and gains (losses) recorded
Asset write-down				19,700
Nonrecurring
Assets at fair value and gains (losses) recorded
Equipment held for lease	5,619		5,619		23,255
Equipment held for sale	2,110		2,110		39,261
Spare parts inventory	934		934		5,336
Assets at fair value	8,663		8,663		67,852
Total losses on equipment held for lease			(3,434)	(9,019)
Total losses on equipment held for sale			(1,359)	(10,649)
Total losses on spare parts inventory			(2,169)	(2,575)
Total losses on assets			(6,962)	$ (22,243)
Nonrecurring | Level 2
Assets at fair value and gains (losses) recorded
Equipment held for lease	5,619		5,619		23,255
Equipment held for sale	2,110		2,110		39,261
Spare parts inventory	934		934		5,336
Assets at fair value	$ 8,663		$ 8,663		$ 67,852