Fair Value - Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financial assets not carried at fair value:
HTM debt securities	$ 493,123	$ 544,280
Carrying Value
Financial assets not carried at fair value:
Loans held-for-investment and loans held-for-sale	13,285,752	11,116,929
HTM debt securities	486,734	538,605
Financial liabilities not carried at fair value:
Secured financing agreements, CLOs and SASB	14,116,282	11,076,744
Unsecured senior notes	1,733,684	1,732,520
Fair Value
Financial assets not carried at fair value:
Loans held-for-investment and loans held-for-sale	13,355,441	11,107,316
HTM debt securities	467,157	515,253
Financial liabilities not carried at fair value:
Secured financing agreements, CLOs and SASB	14,220,699	11,108,364
Unsecured senior notes	$ 1,805,826	$ 1,786,667