Loans Receivable - Overall Statistics for Loans Receivable Portfolio (Detail) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015 USD ($) SecurityLoan	Dec. 31, 2014 USD ($) SecurityLoan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	138	60
Principal Balance	$ 10,169,609	$ 4,462,897
Net book value	10,131,323	$ 4,428,500
Unfunded loan commitments	$ 791,200
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	138	60
Principal Balance	$ 10,169,609	$ 4,462,897
Net book value	10,131,323	4,428,500
Unfunded loan commitments	$ 791,154	$ 513,229
Weighted-average maximum maturity (years)	3 years 4 months 24 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	4.72%	4.36%
Weighted-average all-in yield, rate	5.06%	4.81%
Floating Rate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	101
Principal Balance	$ 8,009,046
Net book value	7,969,227
Unfunded loan commitments	$ 786,419
Weighted-average cash coupon	L+4.21 %
Weighted-average all-in yield	L+4.59 %
Weighted-average maximum maturity (years)	3 years 6 months
Fixed Rate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | SecurityLoan	37
Principal Balance	$ 2,160,563
Net book value	2,162,096
Unfunded loan commitments	$ 4,735
Weighted-average maximum maturity (years)	2 years 10 months 24 days
Fixed Rate Loans [Member] | LIBOR [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average cash coupon, rate	5.33%
Weighted-average all-in yield, rate	5.54%