Gross Realized Gains and Losses on Sales and Calls of Available for Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	$ 193	$ 12,000	$ 6,989	$ 12,231	$ 14,774
Gross realized losses					(1,600)
Total Realized Gains on Sales and Calls of AFS Securities, net	526		6,989	12,564	13,287
Call Option
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	$ 333			$ 333	$ 113