Fair Value - Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financial assets not carried at fair value:
HTM securities	$ 327,831	$ 321,244
Financial liabilities not carried at fair value:
Convertible senior notes	1,329,072	1,323,795
Carrying Value
Financial assets not carried at fair value:
Loans held-for-investment and loans transferred as secured borrowings	6,276,166	6,059,652
HTM securities	327,831	321,244
European servicing rights	2,122	2,626
Financial liabilities not carried at fair value:
Secured financing agreements and secured borrowings on transferred loans	4,570,865	4,068,699
Convertible senior notes	1,329,072	1,323,795
Fair Value.
Financial assets not carried at fair value:
Loans held-for-investment and loans transferred as secured borrowings	6,339,187	6,125,881
HTM securities	315,171	315,255
European servicing rights	4,895	5,302
Financial liabilities not carried at fair value:
Secured financing agreements and secured borrowings on transferred loans	4,568,435	4,092,264
Convertible senior notes	$ 1,292,296	$ 1,331,979