Loan Balances and Related Allowance for Loan Losses, by Portfolio Type (Detail) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, balance at beginning of period	$ 13,634,000	$ 15,627,000	$ 18,101,000
Charged off loans	(991,000)	(2,661,000)	(2,736,000)
Recoveries on loans previously charged off	155,000	232,000	1,095,000
Provision for loan losses	1,850,000	1,450,000	(833,000)
Allowance for loan losses, balance at end of period	14,648,000	14,648,000	15,627,000
Allowance for loans individually evaluated for impairment	4,238,000	4,238,000	2,783,000
Allowance for loans collectively evaluated for impairment	10,410,000	10,410,000	12,844,000
Loans individually evaluated for impairment	36,943,000	36,943,000	18,395,000
Loans collectively evaluated for impairment	671,455,000	671,455,000	639,884,000
Ending balance	708,398,000	708,398,000	658,279,000
Commercial loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, balance at beginning of period	6,223,000	8,908,000	10,017,000
Charged off loans	(948,000)	(1,668,000)	(1,218,000)
Recoveries on loans previously charged off	148,000	221,000	1,067,000
Provision for loan losses	2,985,000	947,000	(958,000)
Allowance for loan losses, balance at end of period	8,408,000	8,408,000	8,908,000
Allowance for loans individually evaluated for impairment	4,049,000	4,049,000	1,648,000
Allowance for loans collectively evaluated for impairment	4,359,000	4,359,000	7,260,000
Loans individually evaluated for impairment	18,761,000	18,761,000	5,140,000
Loans collectively evaluated for impairment	154,876,000	154,876,000	174,165,000
Ending balance	173,637,000	173,637,000	179,305,000
Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, balance at beginning of period	6,363,000	5,777,000	6,351,000
Charged off loans		(655,000)	(1,315,000)
Recoveries on loans previously charged off		1,000	3,000
Provision for loan losses	(1,459,000)	(219,000)	738,000
Allowance for loan losses, balance at end of period	4,904,000	4,904,000	5,777,000
Allowance for loans individually evaluated for impairment	189,000	189,000	1,135,000
Allowance for loans collectively evaluated for impairment	4,715,000	4,715,000	4,642,000
Loans individually evaluated for impairment	16,921,000	16,921,000	10,088,000
Loans collectively evaluated for impairment	371,166,000	371,166,000	348,230,000
Ending balance	388,087,000	388,087,000	358,318,000
Land development loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, balance at beginning of period	265,000	316,000	830,000
Charged off loans	(29,000)	(80,000)	(138,000)
Recoveries on loans previously charged off		0
Provision for loan losses	490,000	490,000	(376,000)
Allowance for loan losses, balance at end of period	726,000	726,000	316,000
Allowance for loans collectively evaluated for impairment	726,000	726,000	316,000
Loans individually evaluated for impairment	528,000	528,000	2,597,000
Loans collectively evaluated for impairment	26,960,000	26,960,000	25,088,000
Ending balance	27,488,000	27,488,000	27,685,000
Consumer and Single Family Mortgages
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, balance at beginning of period	783,000	626,000	903,000
Charged off loans	(14,000)	(258,000)	(65,000)
Recoveries on loans previously charged off	7,000	10,000	25,000
Provision for loan losses	(166,000)	232,000	(237,000)
Allowance for loan losses, balance at end of period	610,000	610,000	626,000
Allowance for loans collectively evaluated for impairment	610,000	610,000	626,000
Loans individually evaluated for impairment	733,000	733,000	570,000
Loans collectively evaluated for impairment	118,453,000	118,453,000	92,401,000
Ending balance	$ 119,186,000	$ 119,186,000	$ 92,971,000