Other Comprehensive Income (Loss) - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Amounts Reclassified Out Of Accumulated Other Comprehensive Income Loss [Abstract]
Reclassification adjustment for gains realized in income	$ (1,857,000)	$ (3,555,000)	$ (2,578,000)	$ (3,969,000)
Other than temporary impairment of securities available for sale	$ 0	$ 0	$ 0	$ 0