Loans - Allowances for Loan Losses and Ending Balances by Portfolio Segment and Based on Impairment Method (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Ending allowance balances attributable to loans:
Individually evaluated for impairment	$ 921		$ 779
Collectively evaluated for impairment	4,024		3,801
Total ending allowance balance	4,945	4,804	4,580	4,471	4,246	4,082
Loans:
Loans individually evaluated for impairment	8,696		10,191
Loans collectively evaluated for impairment	369,247		354,150
Total ending loans balance	377,943		364,341
Commercial [Member]
Ending allowance balances attributable to loans:
Individually evaluated for impairment	194		85
Collectively evaluated for impairment	1,122		848
Total ending allowance balance	1,316	1,176	933	896	976	1,024
Loans:
Loans individually evaluated for impairment	3,504		4,315
Loans collectively evaluated for impairment	113,394		100,584
Total ending loans balance	116,898		104,899
Commercial Real Estate [Member]
Ending allowance balances attributable to loans:
Individually evaluated for impairment	463		522
Collectively evaluated for impairment	1,352		1,380
Total ending allowance balance	1,815	1,824	1,902	1,927	1,649	1,673
Loans:
Loans individually evaluated for impairment	3,502		4,573
Loans collectively evaluated for impairment	125,511		114,619
Total ending loans balance	129,013		119,192
Residential Real Estate [Member]
Ending allowance balances attributable to loans:
Individually evaluated for impairment	264		172
Collectively evaluated for impairment	910		924
Total ending allowance balance	1,174	1,282	1,096	1,051	939	894
Loans:
Loans individually evaluated for impairment	1,690		1,137
Loans collectively evaluated for impairment	109,496		109,275
Total ending loans balance	111,186		110,412
Construction & Land Development [Member]
Ending allowance balances attributable to loans:
Collectively evaluated for impairment	162		253
Total ending allowance balance	162	134	253	217	184	180
Loans:
Loans individually evaluated for impairment			166
Loans collectively evaluated for impairment	14,056		23,192
Total ending loans balance	14,056		23,358
Consumer [Member]
Ending allowance balances attributable to loans:
Collectively evaluated for impairment	144		76
Total ending allowance balance	144	68	76	64	74	78
Loans:
Loans collectively evaluated for impairment	6,790		6,480
Total ending loans balance	6,790		6,480
Unallocated [Member]
Ending allowance balances attributable to loans:
Collectively evaluated for impairment	334		320
Total ending allowance balance	$ 334	$ 320	$ 320	$ 316	$ 424	$ 233