Fair Values - Schedule of Details of Carrying Amount, Face Amount, and Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015	Nov. 30, 2013
Financial assets
Cash and cash equivalents, face amount	$ 64,275	$ 75,567	$ 110,622	$ 96,450
Loans receivable, net, face amount	8,759,696	8,727,218
Financial liabilities
Secured debt agreements, net, face amount	5,776,165	5,731,626
Loan participations sold, net	354,131	348,077
Loan participations sold, net, face amount	426,700	419,560
Carrying Amount [Member]
Financial assets
Cash and cash equivalents	64,275	75,567
Loans receivable, net	8,721,768	8,692,978
Financial liabilities
Secured debt agreements, net	5,760,191	5,716,354
Loan participations sold, net	354,131	348,077
Convertible notes, net	167,475	166,762
Fair Value [Member]
Financial assets
Cash and cash equivalents	64,275	75,567
Loans receivable, net	8,765,688	8,733,784
Financial liabilities
Secured debt agreements, net	5,776,165	5,731,626
Loan participations sold, net	355,583	349,633
Convertible notes, net	194,870	191,763
Senior Participation [Member]
Financial liabilities
Loan participations sold, net	354,131	348,077
Loan participations sold, net, face amount	355,583	349,633
5.25% Convertible Senior Notes [Member]
Financial liabilities
Convertible notes, net, face amount	$ 172,500	$ 172,500			$ 172,500