Non-Accrual Status of Investments (Detail) - Dec. 31, 2014 - USD ($) $ in Thousands		Total
Investment Holdings [Line Items]
Weighted Average Coupon	[1]	3.60%
Other securities
Investment Holdings [Line Items]
Principal/Par Amount on Non Accrual		$ 210,600
Weighted Average Coupon		3.50%
Fair Value		$ 17,120
CMBS receivables
Investment Holdings [Line Items]
Principal/Par Amount on Non Accrual		$ 5,000
Weighted Average Coupon		5.70%
Fair Value		$ 1,250

[1] Weighted-average coupon is calculated on the unpaid principal amount of the underlying instruments, which does not necessarily correspond to the carrying amount.