Shareholder's Equity - Actual Capital Amounts and Ratios and Required Minimum Capital Amounts and Ratios and Capital Amounts and Ratios to be Well Capitalized (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (to Risk Weighted Assets) Actual Amount	$ 100,243	$ 111,141	$ 112,342
Tier 1 Capital (to Risk Weighted Assets) Actual Amount	94,493	105,009	105,728
Tier 1 Capital (to Average Assets) Actual Amount	94,493	105,009	105,728
Total Capital (to Risk Weighted Assets) Actual Ratio	21.95%	22.79%	21.29%
Tier 1 Capital (to Risk Weighted Assets) Actual Ratio	20.70%	21.54%	20.04%
Tier 1 Capital (to Average Assets) Actual Ratio	13.29%	13.48%	13.07%
Total Capital (to Risk Weighted Assets) For Capital Adequacy Purpose Amount	36,528	39,022	42,216
Tier 1 Capital (to Risk Weighted Assets) For Capital Adequacy Purpose Amount	18,264	19,511	21,108
Tier 1 Capital (to Average Assets) For Capital Adequacy Purpose Amount	28,437	31,170	32,361
Total Capital (to Risk Weighted Assets) For Capital Adequacy Purpose Ratio	8.00%	8.00%	8.00%
Tier 1 Capital (to Risk Weighted Assets) For Capital Adequacy Purpose Ratio	4.00%	4.00%	4.00%
Tier 1 Capital (to Average Assets) For Capital Adequacy Purpose Ratio	4.00%	4.00%	4.00%
Total Capital (to Risk Weighted Assets) Well Capitalized Ratio	10.00%
Tier One Capital to Risk Weighted Assets to Well capitalized Ratio	6.00%
Tier One Capital to Average Assets to Well Capitalized Amount	5.00%
Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (to Risk Weighted Assets) Actual Amount	96,427	106,870	107,885
Tier 1 Capital (to Risk Weighted Assets) Actual Amount	90,720	100,746	101,241
Tier 1 Capital (to Average Assets) Actual Amount	90,720	100,746	101,241
Total Capital (to Risk Weighted Assets) Actual Ratio	21.28%	21.94%	20.47%
Tier 1 Capital (to Risk Weighted Assets) Actual Ratio	20.02%	20.69%	19.22%
Tier 1 Capital (to Average Assets) Actual Ratio	13.15%	13.02%	12.62%
Total Capital (to Risk Weighted Assets) For Capital Adequacy Purpose Amount	36,247	38,968	42,148
Tier 1 Capital (to Risk Weighted Assets) For Capital Adequacy Purpose Amount	18,124	19,484	21,074
Tier 1 Capital (to Average Assets) For Capital Adequacy Purpose Amount	27,599	30,958	32,086
Total Capital (to Risk Weighted Assets) For Capital Adequacy Purpose Ratio	8.00%	8.00%	8.00%
Tier 1 Capital (to Risk Weighted Assets) For Capital Adequacy Purpose Ratio	4.00%	4.00%	4.00%
Tier 1 Capital (to Average Assets) For Capital Adequacy Purpose Ratio	4.00%	4.00%	4.00%
Total Capital (to Risk Weighted Assets) Well Capitalized Amount	45,309	48,711	52,685
Tier 1 Capital (to Risk Weighted Assets) Well Capitalized Amount	27,186	29,227	31,611
Tier 1 Capital (to Average Assets) to Well Capitalized Amount	$ 34,499	$ 38,697	$ 40,108
Total Capital (to Risk Weighted Assets) Well Capitalized Ratio	10.00%	10.00%	10.00%
Tier One Capital to Risk Weighted Assets to Well capitalized Ratio	6.00%	6.00%	6.00%
Tier One Capital to Average Assets to Well Capitalized Amount	5.00%	5.00%	5.00%