Mortgage-Backed Securities - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Schedule of Available-for-sale Securities [Line Items]
Net unrealized gains (losses) from other comprehensive income into gain (loss) on sale of investments	$ (20,766,000)	$ 5,692,000	$ (32,484,000)	$ 12,404,000
Agency RMBS
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses			117,700,000
Agency-CMO, Non-Agency RMBS And CMBS
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses			$ 52,300,000