Fair Values - Schedule of Details of Book Value, Face Amount, and Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financial assets
Cash and cash equivalents	$ 289,970	$ 150,090
Loans receivable, net	16,652,824	16,277,343
Debt securities held-to-maturity	79,200	88,958
Financial liabilities
Secured debt agreements, net, face amount	7,896,863	9,753,059
Securitized debt obligations, net	2,922,499	1,187,084
Securitized debt obligations, net,face amount	2,940,638	1,189,642
Secured term loans, net	1,062,766	746,878
Asset-specific debt agreements, net	391,269	323,504
Asset-specific debt agreements, net, face amount	399,699	330,879
Book Value [Member]
Financial assets
Cash and cash equivalents	289,970	150,090
Loans receivable, net	16,399,166	16,164,801
Debt securities held-to-maturity	75,722	86,638
Financial liabilities
Secured debt agreements, net	7,880,536	9,731,426
Securitized debt obligations, net	2,922,499	1,187,084
Secured term loans, net	1,041,704	736,142
Convertible notes, net	616,389	613,071
Asset-specific debt agreements, net	391,269	323,504
Fair Value [Member]
Financial assets
Cash and cash equivalents	289,970	150,090
Loans receivable, net	16,447,192	16,279,904
Debt securities held-to-maturity	70,127	88,305
Financial liabilities
Secured debt agreements, net	7,896,863	9,753,059
Securitized debt obligations, net	2,923,489	1,189,368
Secured term loans, net	1,053,060	750,769
Convertible notes, net	621,568	665,900
Asset-specific debt agreements, net	399,699	330,879
Convertible Senior Note [Member]
Financial liabilities
Convertible notes, net, face amount	$ 622,500	$ 622,500