Loans - Allowances for Loan Losses and Ending Balances by Portfolio Segment and Based on Impairment Method (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Ending allowance balances attributable to loans:
Individually evaluated for impairment	$ 919		$ 779
Collectively evaluated for impairment	4,158		3,801
Total ending allowance balance	5,077	4,945	4,580	4,661	4,471	4,082
Loans:
Loans individually evaluated for impairment	9,190		10,191
Loans collectively evaluated for impairment	367,984		354,150
Total ending loans balance	377,174		364,341
Commercial [Member]
Ending allowance balances attributable to loans:
Individually evaluated for impairment	185		85
Collectively evaluated for impairment	1,109		848
Total ending allowance balance	1,294	1,316	933	992	896	1,024
Loans:
Loans individually evaluated for impairment	3,898		4,315
Loans collectively evaluated for impairment	112,292		100,584
Total ending loans balance	116,190		104,899
Commercial Real Estate [Member]
Ending allowance balances attributable to loans:
Individually evaluated for impairment	442		522
Collectively evaluated for impairment	1,368		1,380
Total ending allowance balance	1,810	1,815	1,902	2,035	1,927	1,673
Loans:
Loans individually evaluated for impairment	3,460		4,573
Loans collectively evaluated for impairment	122,963		114,619
Total ending loans balance	126,423		119,192
Residential Real Estate [Member]
Ending allowance balances attributable to loans:
Individually evaluated for impairment	292		172
Collectively evaluated for impairment	952		924
Total ending allowance balance	1,244	1,174	1,096	1,016	1,051	894
Loans:
Loans individually evaluated for impairment	1,832		1,137
Loans collectively evaluated for impairment	110,987		109,275
Total ending loans balance	112,819		110,412
Construction & Land Development [Member]
Ending allowance balances attributable to loans:
Individually evaluated for impairment
Collectively evaluated for impairment	180		253
Total ending allowance balance	180	162	253	302	217	180
Loans:
Loans individually evaluated for impairment			166
Loans collectively evaluated for impairment	14,904		23,192
Total ending loans balance	14,904		23,358
Consumer [Member]
Ending allowance balances attributable to loans:
Individually evaluated for impairment
Collectively evaluated for impairment	92		76
Total ending allowance balance	92	144	76	82	64	78
Loans:
Loans individually evaluated for impairment
Loans collectively evaluated for impairment	6,838		6,480
Total ending loans balance	6,838		6,480
Unallocated [Member]
Ending allowance balances attributable to loans:
Individually evaluated for impairment
Collectively evaluated for impairment	457		320
Total ending allowance balance	457	334	320	234	316	233
Loans:
Loans individually evaluated for impairment
Loans collectively evaluated for impairment
Total ending loans balance