Secured Financing Agreements - Principal Repayments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Repayment of secured financings
Total	$ 2,073,229		$ 2,073,229		$ 2,053,229
Secured financing agreements
Repayment of secured financings
2017 (remainder of)	795,722		795,722
2018	1,065,120		1,065,120
2019	397,070		397,070
2020	1,399,582		1,399,582
2021	568,104		568,104
Thereafter	1,330,122		1,330,122
Total	5,555,720		5,555,720		$ 4,197,218
Amortization of deferred financing costs from secured financing agreements included in interest expense	5,000	$ 3,900	14,400	$ 12,100
Repurchase Agreements
Repayment of secured financings
2017 (remainder of)	781,261		781,261
2018	988,168		988,168
2019	395,715		395,715
2020	1,041,480		1,041,480
2021	2,289		2,289
Thereafter	82,611		82,611
Total	3,291,524		3,291,524
Other Secured Financing
Repayment of secured financings
2017 (remainder of)	14,461		14,461
2018	76,952		76,952
2019	1,355		1,355
2020	358,102		358,102
2021	565,815		565,815
Thereafter	1,247,511		1,247,511
Total	$ 2,264,196		$ 2,264,196