Fair Values - Schedule of Details of Book Value, Face Amount, and Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financial assets
Cash and cash equivalents	$ 1,259,836	$ 150,090
Loans receivable, net	16,434,631	16,277,343
Debt securities held-to-maturity	82,002	88,958
Financial liabilities
Secured debt agreements, net, face amount	9,716,452	10,083,938
Securitized debt obligations, net	2,240,612	1,187,084
Securitized debt obligations, net,face amount	2,253,008	1,189,642
Secured term loans, net	1,068,134	746,878
Book Value [Member]
Financial assets
Cash and cash equivalents	1,259,836	150,090
Loans receivable, net	16,161,353	16,164,801
Debt securities held-to-maturity	75,836	86,638
Financial liabilities
Secured debt agreements, net	9,689,541	10,054,930
Securitized debt obligations, net	2,240,612	1,187,084
Secured term loans, net	1,045,163	736,142
Convertible notes, net	614,710	613,071
Fair Value [Member]
Financial assets
Cash and cash equivalents	1,259,836	150,090
Loans receivable, net	16,214,574	16,279,904
Debt securities held-to-maturity	68,940	88,305
Financial liabilities
Secured debt agreements, net	9,716,452	10,083,938
Securitized debt obligations, net	2,172,578	1,189,368
Secured term loans, net	1,012,228	750,769
Convertible notes, net	580,810	665,900
Convertible Senior Note [Member]
Financial liabilities
Convertible notes, net, face amount	$ 622,500	$ 622,500