Fair Values - Schedule of Details of Book Value, Face Amount, and Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financial assets
Cash and cash equivalents	$ 289,552	$ 289,970
Loans receivable, net	17,529,542	16,652,824
Debt securities held-to-maturity	79,200	79,200
Financial liabilities
Secured debt agreements, net, face amount	8,729,281	7,896,863
Securitized debt obligations, net	2,833,778	2,922,499
Securitized debt obligations, net,face amount	2,855,625	2,940,638
Term loans, net	1,356,140	1,062,766
Asset-specific debt , net, face amount	299,601	399,699
Book Value [Member]
Financial assets
Cash and cash equivalents	289,552	289,970
Loans receivable, net	17,307,898	16,399,166
Debt securities held-to-maturity	77,632	75,722
Financial liabilities
Secured debt, net	8,709,818	7,880,536
Securitized debt obligations, net	2,833,778	2,922,499
Asset-specific debt , net	292,122	391,269
Term loans, net	1,332,130	1,041,704
Convertible notes, net	618,111	616,389
Fair Value [Member]
Financial assets
Cash and cash equivalents	289,552	289,970
Loans receivable, net	17,342,841	16,447,192
Debt securities held-to-maturity	78,835	70,127
Financial liabilities
Secured debt, net	8,729,281	7,896,863
Securitized debt obligations, net	2,055,287	2,923,489
Asset-specific debt , net	299,601	399,699
Term loans, net	1,347,533	1,053,060
Convertible notes, net	637,303	621,568
Convertible Senior Note [Member]
Financial liabilities
Convertible notes, net, face amount	$ 622,500	$ 622,500