Investment Securities - Gross Unrealized Losses and Fair Value for Investment Securities by Investment Category and Continuous Unrealized Loss Position Time (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than Twelve Months, Fair Value	$ 101,336	$ 33,466
Available-for-sale securities, Less than Twelve Months, Gross Unrealized Losses	(4,125)	(114)
Available-for-sale securities, Twelve Months or Greater, Fair Value		82
Available-for-sale securities, Twelve Months or Greater, Gross Unrealized Losses		(1)
Available-for-sale securities, Total, Fair Value	101,336	33,548
Available-for-sale securities, Total, Gross Unrealized Losses	(4,125)	(115)
U.S. Government Corporations and Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than Twelve Months, Fair Value	42,009	6,993
Available-for-sale securities, Less than Twelve Months, Gross Unrealized Losses	(1,580)	(7)
Available-for-sale securities, Twelve Months or Greater, Fair Value
Available-for-sale securities, Twelve Months or Greater, Gross Unrealized Losses
Available-for-sale securities, Total, Fair Value	42,009	6,993
Available-for-sale securities, Total, Gross Unrealized Losses	(1,580)	(7)
Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than Twelve Months, Fair Value	11,964	2,721
Available-for-sale securities, Less than Twelve Months, Gross Unrealized Losses	(763)	(55)
Available-for-sale securities, Twelve Months or Greater, Fair Value
Available-for-sale securities, Twelve Months or Greater, Gross Unrealized Losses
Available-for-sale securities, Total, Fair Value	11,964	2,721
Available-for-sale securities, Total, Gross Unrealized Losses	(763)	(55)
Mortgage-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than Twelve Months, Fair Value	47,330	23,752
Available-for-sale securities, Less than Twelve Months, Gross Unrealized Losses	(1,781)	(52)
Available-for-sale securities, Twelve Months or Greater, Fair Value		82
Available-for-sale securities, Twelve Months or Greater, Gross Unrealized Losses		(1)
Available-for-sale securities, Total, Fair Value	47,330	23,834
Available-for-sale securities, Total, Gross Unrealized Losses	(1,781)	(53)
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than Twelve Months, Fair Value	33
Available-for-sale securities, Less than Twelve Months, Gross Unrealized Losses	(1)
Available-for-sale securities, Twelve Months or Greater, Fair Value
Available-for-sale securities, Twelve Months or Greater, Gross Unrealized Losses
Available-for-sale securities, Total, Fair Value	33
Available-for-sale securities, Total, Gross Unrealized Losses	$ (1)