Investment Securities - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013 Securities	Mar. 31, 2012	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Securities issued by U.S. government percentage	74.00%
Gains (loss) recognized	$ 0	$ 0
Number of securities	13
Investment securities, par value	$ 94,200,000
Pre-tax gain on sale of securities	2,094,000
Gross Unrealized Holding Losses	0
Credit-related impairment loss on investment securities held-to-maturity
Average life of investment grade debt securities, years	4 years 2 months 12 days
Investment securities pledged as collateral	2,300,000,000		2,240,000,000
Government agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Agency bond callable	162,100,000
CMO's / REMIC's - residential [Member]
Schedule of Available-for-sale Securities [Line Items]
CMO/REMIC's backed by whole loans issued by private-label companies (non-government sponsored)	1,100,000		1,200,000
Investment security classified as held-to-maturity, number	1
Held-to-Maturity securities, average FICO score	715
Held-to-Maturity securities, acquired price, percentage	98.25%
Average percentage of LTV	71.00%
Current fair value percentage of Held-to-Maturity security against par value	72.00%
Investment contractual cash flows guaranteed by Government, percentage	99.92%
Investment contractual cash flows guaranteed by banks, percentage	0.08%
Municipal bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Average life of investment grade debt securities, years	9 years 3 months 18 days
Alt-A bond [Member]
Schedule of Available-for-sale Securities [Line Items]
Book value of the bond	2,000,000
Net impairment losses	$ 1,900,000