Loans Receivable - Overall Statistics for Loans Receivable Portfolio (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) SecurityLoan	Dec. 31, 2014 USD ($) SecurityLoan	Dec. 31, 2013 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 9,077,007	$ 4,428,500
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	125	60
Principal Balance	$ 9,108,361	$ 4,462,897	$ 2,077,227
Net book value	9,077,007	4,428,500
Unfunded loan commitments	$ 700,658	$ 513,229
Weighted-average maximum maturity (years)	3 years 1 month 6 days	3 years 10 months 24 days
Loans Receivable [Member] | LIBOR [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average cash coupon, rate	4.84%	4.36%
Weighted-average all-in yield, rate	5.18%	4.81%
Floating Rate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	92
Principal Balance	$ 7,098,180
Net book value	7,064,279
Unfunded loan commitments	$ 696,276
Weighted-average cash coupon	L+4.09 %
Weighted-average all-in yield	L+4.49 %
Weighted-average maximum maturity (years)	3 years 3 months 18 days
Floating Rate [Member] | LIBOR [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average cash coupon, rate	4.09%
Weighted-average all-in yield, rate	4.49%
Fixed Rate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	33
Principal Balance	$ 2,010,181
Net book value	2,012,728
Unfunded loan commitments	$ 4,382
Weighted-average maximum maturity (years)	2 years 7 months 6 days
Fixed Rate [Member] | LIBOR [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average cash coupon, rate	5.63%
Weighted-average all-in yield, rate	5.78%