Fair Values - Schedule of Details of Book Value, Face Amount, and Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financial assets
Cash and cash equivalents	$ 280,126	$ 289,970
Loans receivable, net	17,143,102	16,652,824
Debt securities held-to-maturity	79,200	79,200
Financial liabilities
Secured debt agreements, net, face amount	8,142,728	7,896,863
Securitized debt obligations, net	2,875,241	2,922,499
Asset-specific debt agreements, net	430,448	391,269
Securitized debt obligations, net,face amount	2,891,785	2,940,638
Secured term loans, net	1,259,575	1,062,766
Asset-specific debt agreements, net, face amount	438,433	399,699
Book Value [Member]
Financial assets
Cash and cash equivalents	280,126	289,970
Loans receivable, net	16,888,002	16,399,166
Debt securities held-to-maturity	76,708	75,722
Financial liabilities
Secured debt agreements, net	8,124,787	7,880,536
Securitized debt obligations, net	2,875,241	2,922,499
Asset-specific debt agreements, net	430,448	391,269
Secured term loans, net	1,235,808	1,041,704
Convertible notes, net	617,242	616,389
Fair Value [Member]
Financial assets
Cash and cash equivalents	280,126	289,970
Loans receivable, net	16,954,287	16,447,192
Debt securities held-to-maturity	73,667	70,127
Financial liabilities
Secured debt agreements, net	8,142,728	7,896,863
Securitized debt obligations, net	2,890,537	2,923,489
Asset-specific debt agreements, net	438,433	399,699
Secured term loans, net	1,250,356	1,053,060
Convertible notes, net	639,223	621,568
Convertible Senior Note [Member]
Financial liabilities
Convertible notes, net, face amount	$ 622,500	$ 622,500