Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Income Tax Expense Benefit [Line Items]
Allowance for loan losses	$ 6,508	$ 5,861
Basis adjustments on loans	1,720	1,337
Reserve for self-funded insurance	183	146
Oregon purchased tax credits	2,951	4,009
Nonqualified stock options	957	694
Accrued compensation	647	557
OTTI credit impairment	80	80
Nonaccrual loan interest	21	141
Other	47	11
Total deferred tax assets	13,114	12,836
Federal Home Loan Bank stock dividends	595	595
Excess tax over book depreciation	1,446	1,485
Prepaid expenses	362	330
NWBF acquisition adjustments		80
Loan origination fees	881	832
Net unrealized gains on securities	3,600	2,206
Total deferred tax liabilities	6,884	5,528
Net deferred tax assets	$ 6,230	$ 7,308