Loans Receivable - Performing and Nonperforming Single Family Residential and Consumer Loans Based on Payment Activity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Residential Real Estate, Single Family [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$ 335,419	$ 326,005
Residential Real Estate, Single Family [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	331,904	322,662
Residential Real Estate, Single Family [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,515	3,343
Consumer Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	82,193	80,418
Consumer Home Equity [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	81,892	80,124
Consumer Home Equity [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	301	294
Dealer Auto and RV Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	48,003	46,571
Dealer Auto and RV Loans [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	47,832	46,450
Dealer Auto and RV Loans [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	171	121
Other Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,097	7,896
Other Consumer [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,017	7,787
Other Consumer [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$ 80	$ 109