Investment Securities Available for Sale - Amortized Cost and Estimated Market Value of Investment Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 236,437	$ 223,953
Gross Unrealized Gains	1,274	1,374
Gross Unrealized Losses	(10,958)	(11,734)
Estimated Market Value	226,753	213,593
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	148,199	138,105
Gross Unrealized Gains	479	945
Gross Unrealized Losses	(376)
Estimated Market Value	148,302	139,050
State and Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27,047	25,856
Gross Unrealized Gains	14	5
Gross Unrealized Losses	(116)	(81)
Estimated Market Value	26,945	25,780
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	55,000	55,000
Gross Unrealized Losses	(10,438)	(11,530)
Estimated Market Value	44,562	43,470
Equity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,191	4,992
Gross Unrealized Gains	781	424
Gross Unrealized Losses	(28)	(123)
Estimated Market Value	$ 6,944	$ 5,293