Fair Value Measurements - Reconciliation of Level III Items (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance	$ 36,153	$ 35,333
Amortization of core deposit intangible	(119)	(268)
Increase in impaired loans	1,749	3,895
Decrease in impaired loans	(1,247)	(1,661)
Payments received	(1,953)	(2,646)
Purchases	6,874	1,500
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	34,583	36,153
Core Deposit Intangible [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance	838	1,106
Amortization of core deposit intangible	(119)	(268)
Increase in impaired loans
Decrease in impaired loans
Payments received
Purchases
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	719	838
Goodwill [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance	26,398	26,398
Amortization of core deposit intangible
Increase in impaired loans
Decrease in impaired loans
Payments received
Purchases
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	26,398	26,398
Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance	4,045	2,876
Amortization of core deposit intangible
Increase in impaired loans	1,749	3,895
Decrease in impaired loans	(1,247)	(1,661)
Payments received	(873)	(1,065)
Purchases
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	3,674	4,045
Federal Home Loan Bank Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance	4,212	4,953
Amortization of core deposit intangible
Increase in impaired loans
Decrease in impaired loans
Payments received	(1,080)	(1,581)
Purchases		840
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	3,132	4,212
Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance	660
Amortization of core deposit intangible
Increase in impaired loans
Decrease in impaired loans
Payments received
Purchases		660
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	$ 660	$ 660