Loans Receivable, Net - Overall Statistics for Loans Receivable Portfolio (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) SecurityLoan	Dec. 31, 2015 USD ($) SecurityLoan	Dec. 31, 2014 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	107	125
Net book value	$ 8,692,978	$ 9,077,007
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	107	125
Principal balance	$ 8,727,218	$ 9,108,361	$ 4,462,897
Unfunded loan commitments	$ 882,472	$ 700,658
Weighted-average maximum maturity (years)	3 years 2 months 12 days	3 years 1 month 6 days
Loans Receivable [Member] | LIBOR [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average cash coupon, rate	5.01%	4.84%
Weighted-average all-in yield, rate	5.36%	5.18%
Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 8,692,978	$ 9,077,007	$ 4,428,500