Fair Value - Fair Value Measurements for Items Measured at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member]	Sep. 30, 2012 Fair Value, Measurements, Recurring [Member]	Sep. 30, 2013 Fair Value, Measurements, Nonrecurring [Member]	Sep. 30, 2012 Fair Value, Measurements, Nonrecurring [Member]	Sep. 30, 2013 Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] Fair Value, Measurements, Recurring [Member]	Sep. 30, 2012 Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] Fair Value, Measurements, Recurring [Member]	Sep. 30, 2013 Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] Fair Value, Measurements, Nonrecurring [Member]	Sep. 30, 2012 Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] Fair Value, Measurements, Nonrecurring [Member]	Sep. 30, 2013 Significant Other Observable Inputs (Level 2) [Member] Fair Value, Measurements, Recurring [Member]	Sep. 30, 2012 Significant Other Observable Inputs (Level 2) [Member] Fair Value, Measurements, Recurring [Member]	Sep. 30, 2013 Significant Other Observable Inputs (Level 2) [Member] Fair Value, Measurements, Nonrecurring [Member]	Sep. 30, 2012 Significant Other Observable Inputs (Level 2) [Member] Fair Value, Measurements, Nonrecurring [Member]	Sep. 30, 2013 Significant Unobservable Inputs (Level 3) [Member] Fair Value, Measurements, Recurring [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Fair Value, Measurements, Recurring [Member]	Sep. 30, 2013 Significant Unobservable Inputs (Level 3) [Member] Fair Value, Measurements, Nonrecurring [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member] Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities			$ 650,445	$ 588,248			$ 101	$ 1,711			$ 650,344	$ 586,537			$ 0	$ 0
Loans available for sale			14,322	28,042			0	0			14,322	28,042			0	0
Loans					18,784	22,380			0	0			10,817	10,351			7,967	12,029
Other real estate owned	$ 5,589	$ 11,887			$ 5,589	$ 8,888			$ 0	$ 0			$ 1,046	$ 3,746			$ 4,543	$ 5,142