Investment Securities - Additional Information (Detail) (USD $)				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Maximum	Dec. 31, 2012 Minimum	Dec. 31, 2012 Investments in Debt and Equity Securities, Reported at Less than Historical Cost	Dec. 31, 2011 Investments in Debt and Equity Securities, Reported at Less than Historical Cost	Dec. 31, 2012 U.S. Government-sponsored mortgage-backed securities security	Dec. 31, 2011 U.S. Government-sponsored mortgage-backed securities	Dec. 31, 2012 State and municipal security	Dec. 31, 2012 Trust Preferred Securities
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Historical cost						$ 22,999,000	$ 11,925,000
Fair value	17,038,000	6,339,000				17,038,000	6,339,000	12,320,000	6,176,000	4,524,000
Percent of the Corporation's available for sale and held to maturity portfolio						1.90%	0.70%				1.00%
Investment amortized cost	859,124,000	931,388,000									6,100,000
Fair value of investments											194,000
Spread over LIBOR				1.57%	0.85%
Gross Unrealized losses	5,945,000	5,588,000						46,000	16,000	18,000	5,900,000
Available-for-sale, number of securities in unrealized loss positions								4		8
Gross Unrealized Losses	16,000							15,000		1,000
Held-to-maturity, number of securities in unrealized loss positions								1		4
Book value											6,100,000
Carrying value of securities pledged as collateral	$ 335,775,000	$ 299,478,000	$ 271,091,000