Secured Financings - Summary of Statistics for Asset-Specific Repurchase Agreements (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014 Loans	Dec. 31, 2013 Loans
Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Number of loans	3	4
Principal balance	$ 226,961	$ 245,731
Weighted-average cash coupon	L+2.62 %	L+2.55 %
Weighted-average all-in yield / cost	L+3.00 %	L+3.03 %
Collateral Assets [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted-average cash coupon	2.62%	2.55%
Weighted-average all-in yield / cost	3.00%	3.03%
Assets Sold Under Agreements To Repurchase Carrying Amounts [Member]
Participating Mortgage Loans [Line Items]
Number of loans	4	4
Principal balance	$ 288,831	$ 334,857
Weighted-average cash coupon	L+4.73 %	L+4.79 %
Weighted-average all-in yield / cost	L+5.22 %	L+5.38 %
Assets Sold Under Agreements To Repurchase Carrying Amounts [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted-average cash coupon	4.73%	4.79%
Weighted-average all-in yield / cost	5.22%	5.38%