Loans - Summary of Troubled Debt Restructurings by Collateral Types (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 20,600	$ 23,900	$ 28,200
Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	61	55	45
Troubled debt restructuring loans	18,015	18,744	22,970
Accruing Loans [Member] | Warehouse [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	3	1
Troubled debt restructuring loans	345	1,692	1,341
Accruing Loans [Member] | Raw Land [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	2	5
Troubled debt restructuring loans	1,354	1,337	2,878
Accruing Loans [Member] | Agricultural Land [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1
Troubled debt restructuring loans	66
Accruing Loans [Member] | Hotel & Motel [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	3	3
Troubled debt restructuring loans	2,233	2,318	2,406
Accruing Loans [Member] | Office [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4	4	2
Troubled debt restructuring loans	2,085	2,105	1,513
Accruing Loans [Member] | Retail, including Strip Centers [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	6	6	8
Troubled debt restructuring loans	2,800	2,833	6,228
Accruing Loans [Member] | 1-4 Family Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	34	31	26
Troubled debt restructuring loans	8,061	7,651	8,604
Accruing Loans [Member] | Life Insurance Policy [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1
Troubled debt restructuring loans	249	250
Accruing Loans [Member] | Automobile/Equipment/Inventory [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	5	4
Troubled debt restructuring loans	522	508
Accruing Loans [Member] | Unsecured [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	1
Troubled debt restructuring loans	300	50
Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	9	5	10
Troubled debt restructuring loans	2,568	5,171	5,170
Non-Accruing Loans [Member] | Warehouse [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	2	1
Troubled debt restructuring loans	1,493	177
Non-Accruing Loans [Member] | Raw Land [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1
Troubled debt restructuring loans	29
Non-Accruing Loans [Member] | Office [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts		1	1
Troubled debt restructuring loans		2,770	2,770
Non-Accruing Loans [Member] | Retail, including Strip Centers [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts		1	1
Troubled debt restructuring loans		1,202	45
Non-Accruing Loans [Member] | 1-4 Family Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	6	2	8
Troubled debt restructuring loans	$ 1,046	$ 1,022	$ 2,355