Fair Values - Schedule of Details of Book Value, Face Amount, and Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financial assets
Cash and cash equivalents	$ 211,180	$ 289,970
Loans receivable, net	20,522,560	16,652,824
Debt securities held-to-maturity	79,200	79,200
Financial liabilities
Secured debt agreements, net, face amount	11,188,855	7,896,863
Securitized debt obligations, net	2,836,049	2,922,499
Securitized debt obligations, net,face amount	2,855,625	2,940,638
Term loans, net	1,352,706	1,062,766
Asset-specific debt , net, face amount	328,068	399,699
Book Value [Member]
Financial assets
Cash and cash equivalents	211,180	289,970
Loans receivable, net	20,276,078	16,399,166
Debt securities held-to-maturity	77,636	75,722
Financial liabilities
Secured debt, net	11,170,330	7,880,536
Securitized debt obligations, net	2,836,049	2,922,499
Asset-specific debt , net	320,895	391,269
Term loans, net	1,329,637	1,041,704
Convertible notes, net	618,985	616,389
Fair Value [Member]
Financial assets
Cash and cash equivalents	211,180	289,970
Loans receivable, net	20,358,824	16,447,192
Debt securities held-to-maturity	78,633	70,127
Financial liabilities
Secured debt, net	11,188,855	7,896,863
Securitized debt obligations, net	2,855,589	2,923,489
Asset-specific debt , net	328,068	399,699
Term loans, net	1,343,771	1,053,060
Convertible notes, net	633,845	621,568
Convertible Senior Note [Member]
Financial liabilities
Convertible notes, net, face amount	$ 622,500	$ 622,500