Fair Value - Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financial assets not carried at fair value:
HTM securities	$ 452,725	$ 509,980
Carrying Value
Financial assets not carried at fair value:
Loans held-for-investment and loans transferred as secured borrowings	6,265,819	5,882,995
HTM securities	452,725	509,980
Financial liabilities not carried at fair value:
Secured financing agreements and secured borrowings on transferred loans	4,449,917	4,189,126
Convertible Notes Payable	2,033,384	2,011,544
Fair Value.
Financial assets not carried at fair value:
Loans held-for-investment and loans transferred as secured borrowings	6,320,782	5,934,219
HTM securities	447,723	504,165
Financial liabilities not carried at fair value:
Secured financing agreements and secured borrowings on transferred loans	4,446,571	4,198,136
Convertible Notes Payable	$ 2,092,717	$ 2,088,374