Fair Values - Schedule of Details of Carrying Amount, Face Amount, and Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Financial assets
Cash and cash equivalents, face amount	$ 61,221	$ 75,567	$ 94,061
Restricted cash	32,864
Loans receivable, net, face amount	9,681,055	8,727,218
Financial liabilities
Secured debt agreements, net, face amount	6,096,597	5,731,626
Loan participations sold, net	33,193	348,077
Loan participations sold, net, face amount	93,710	419,560
Securitized debt obligations, net	474,298	0
Securitized debt obligations, net,face amount	474,620
Carrying Amount [Member]
Financial assets
Cash and cash equivalents	61,221	75,567
Restricted cash	32,864
Loans receivable, net	9,637,152	8,692,978
Financial liabilities
Secured debt agreements, net	6,079,135	5,716,354
Loan participations sold, net	33,193	348,077
Securitized debt obligations, net	474,298
Convertible notes, net	562,741	166,762
Fair Value [Member]
Financial assets
Cash and cash equivalents	61,221	75,567
Restricted cash	32,864
Loans receivable, net	9,685,422	8,733,784
Financial liabilities
Secured debt agreements, net	6,096,597	5,731,626
Loan participations sold, net	33,193	349,633
Securitized debt obligations, net	474,655
Convertible notes, net	602,503	191,763
Convertible Senior Note [Member]
Financial liabilities
Convertible notes, net, face amount	575,000	172,500
Senior Participation [Member]
Financial liabilities
Loan participations sold, net	33,193	348,077
Loan participations sold, net, face amount	$ 33,193	$ 349,633