Loans on Nonaccrual Status by Portfolio Type (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Financing Receivable Recorded Investment Nonaccrual Status [Line Items]
Nonaccrual loans	$ 20,894	$ 14,099
Commercial loans
Financing Receivable Recorded Investment Nonaccrual Status [Line Items]
Nonaccrual loans	10,280	4,702
Commercial real estate | Owner occupied
Financing Receivable Recorded Investment Nonaccrual Status [Line Items]
Nonaccrual loans	5,491	2,016
Commercial real estate | All other
Financing Receivable Recorded Investment Nonaccrual Status [Line Items]
Nonaccrual loans	4,071	4,214
Residential mortgage loans | Residential mortgage loans - single family
Financing Receivable Recorded Investment Nonaccrual Status [Line Items]
Nonaccrual loans	524	570
Construction loans
Financing Receivable Recorded Investment Nonaccrual Status [Line Items]
Nonaccrual loans		2,047
Land development loans
Financing Receivable Recorded Investment Nonaccrual Status [Line Items]
Nonaccrual loans	$ 528	$ 550