Fair Value of Assets and Liabilities - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets
Available for sale securities	$ 338,936	$ 356,345
Fair Value, Measurements, Recurring [Member]
Assets
Available for sale securities	338,936	356,345
Bank owned life insurance	9,486	9,323
Liabilities
Interest rate swap	913	1,126
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
Assets
Available for sale securities
Bank owned life insurance
Liabilities
Interest rate swap
Significant Other Observable Inputs (Level 2) [Member]
Assets
Available for sale securities	337,447	354,856
Bank owned life insurance	9,486	9,323
Liabilities
Interest rate swap	913	1,126
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
Assets
Available for sale securities	337,447	354,856
Bank owned life insurance	9,486	9,323
Liabilities
Interest rate swap	913	1,126
Significant Unobservable Inputs (Level 3) [Member]
Assets
Available for sale securities	1,489	1,489
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]
Assets
Available for sale securities	$ 1,489	$ 1,489