Investment Securities Available for Sale - Estimated Market Value and Unrealized Loss for 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]
Less than 12 months, Estimated Market Value	$ 68,594	$ 17,182
Less than 12 months, Unrealized Losses	(518)	(204)
12 months or longer, Estimated Market Value	45,745	43,470
12 months or longer, Unrealized Losses	(10,440)	(11,530)
Total, Estimated Market Value	114,339	60,652
Total, Unrealized Losses	(10,958)	(11,734)
U S Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Market Value	56,007
Less than 12 months, Unrealized Losses	(376)
12 months or longer, Estimated Market Value
12 months or longer, Unrealized Losses
Total, Estimated Market Value	56,007
Total, Unrealized Losses	(376)
State and Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Market Value	11,978	15,918
Less than 12 months, Unrealized Losses	(114)	(81)
12 months or longer, Estimated Market Value	1,183
12 months or longer, Unrealized Losses	(2)
Total, Estimated Market Value	13,161	15,918
Total, Unrealized Losses	(116)	(81)
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Market Value
Less than 12 months, Unrealized Losses
12 months or longer, Estimated Market Value	44,562	43,470
12 months or longer, Unrealized Losses	(10,438)	(11,530)
Total, Estimated Market Value	44,562	43,470
Total, Unrealized Losses	(10,438)	(11,530)
Equity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Estimated Market Value	609	1,264
Less than 12 months, Unrealized Losses	(28)	(123)
12 months or longer, Estimated Market Value
12 months or longer, Unrealized Losses
Total, Estimated Market Value	609	1,264
Total, Unrealized Losses	$ (28)	$ (123)