Loans - Summary of Troubled Debt Restructurings by Collateral Types (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Financing Receivable, Modifications [Line Items]
Troubled debt restructuring loans	$ 23,300	$ 23,900	$ 31,700
Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	52	55	46
Troubled debt restructuring loans	18,513	18,744	26,848
Accruing Loans [Member] | Warehouse [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	3	1
Troubled debt restructuring loans	1,689	1,692	1,343
Accruing Loans [Member] | Raw Land [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	2	4
Troubled debt restructuring loans	1,285	1,337	1,595
Accruing Loans [Member] | Hotel & Motel [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	3	3
Troubled debt restructuring loans	2,273	2,318	2,449
Accruing Loans [Member] | Office [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	4	4	3
Troubled debt restructuring loans	2,095	2,105	1,695
Accruing Loans [Member] | Retail, including Strip Centers [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	6	6	9
Troubled debt restructuring loans	2,821	2,833	6,657
Accruing Loans [Member] | 1-4 Family Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	30	31	25
Troubled debt restructuring loans	7,550	7,651	7,998
Accruing Loans [Member] | Life Insurance Policy [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1
Troubled debt restructuring loans	250	250
Accruing Loans [Member] | Automobile/Equipment/Inventory [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	4
Troubled debt restructuring loans	500	508
Accruing Loans [Member] | Unsecured [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1
Troubled debt restructuring loans	50	50
Accruing Loans [Member] | Apartments [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts			1
Troubled debt restructuring loans			5,111
Non-Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	8	5	9
Troubled debt restructuring loans	4,755	5,171	4,867
Non-Accruing Loans [Member] | Warehouse [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1
Troubled debt restructuring loans	176	177
Non-Accruing Loans [Member] | Raw Land [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1		1
Troubled debt restructuring loans	43		137
Non-Accruing Loans [Member] | Hotel & Motel [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts			1
Troubled debt restructuring loans			2,072
Non-Accruing Loans [Member] | Office [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1	1
Troubled debt restructuring loans	2,450	2,770	103
Non-Accruing Loans [Member] | Retail, including Strip Centers [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1	1
Troubled debt restructuring loans	969	1,202
Non-Accruing Loans [Member] | 1-4 Family Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3	2	6
Troubled debt restructuring loans	1,111	1,022	2,555
Non-Accruing Loans [Member] | Life Insurance Policy [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts
Troubled debt restructuring loans
Non-Accruing Loans [Member] | Automobile/Equipment/Inventory [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1
Troubled debt restructuring loans	6
Non-Accruing Loans [Member] | Unsecured [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts
Troubled debt restructuring loans
Non-Accruing Loans [Member] | Apartments [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts
Troubled debt restructuring loans