Loans and Allowance for Loan Losses - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2012 Loan	Mar. 31, 2012	Jun. 30, 2012 Loan	Dec. 31, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate loans pledged to secured borrowings obtained from Federal Home Loan Bank	$ 141,000,000		$ 141,000,000	$ 161,000,000
Increase in total past due loans			12,600,000
Total past due loans	23,702,000		23,702,000	11,151,000
Increase of Loans past due for 90 days or more			5,700,000
Loans past due 90 days or more	10,794,000		10,794,000	5,110,000
30-59 Days Past Due	9,426,000		9,426,000	1,957,000
Nonaccrual loans	20,894,000		20,894,000	14,099,000
Transfer loan into OREO		2,100,000
Fully collateralized unpaid loan, current	684,696,000		684,696,000	647,128,000
Gross loans	708,398,000		708,398,000	658,279,000
Increase (Decrease) in loan portfolios			50,119,000
Loans, allowances	14,648,000	13,634,000	14,648,000	15,627,000	18,101,000
Ratio of allowance for loan losses to loans outstanding	2.07%	1.98%	2.07%	2.37%
Charge off loans			2,400,000
Increase (decrease) in allowances for credit losses		1,000,000	(1,000,000)
Provision for loan losses			1,400,000
Total impaired loans	38,356,000		38,356,000	18,395,000
Impaired loans with no specific reserves	22,000,000	17,500,000	22,000,000	8,500,000
Investment in impaired loans			27,600,000	27,500,000
Interest that would have been earned had impaired loans remained current in accordance with original terms	151,000		188,000
Troubled debt restructurings	22,360,000		22,360,000	4,214,000
Accruing TDR's	16,180,000		16,180,000
Number of loans added	13		13
Subsequent Event
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	3,400,000		3,400,000
Fully collateralized unpaid loan, current	1,000,000		1,000,000
Principal reduction payment of nonaccrual loans			2,400,000
Increase in nonaccrual loan	6,100,000		6,100,000
Impaired loans less than 90 days delinquent
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (Decrease) in loan portfolios			10,900,000
Total impaired loans	24,163,000		24,163,000	13,285,000
Impaired loans less than 90 days delinquent | Borrower one
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total impaired loans	8,200,000		8,200,000
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase of Loans past due for 90 days or more			5,500,000
Construction loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due loans				2,047,000
Loans past due 90 days or more				2,047,000
Loan transferred into other real estate owned			2,000,000
Nonaccrual loans				2,047,000
Gross loans				2,047,000
Total impaired loans				2,047,000
Investment in impaired loans			1,024,000	2,225,000
Financing Receivable, 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase in total past due loans			7,500,000
30-59 Days Past Due	8,200,000		8,200,000
Specific reserves	2,600,000		2,600,000
Current Performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	6,600,000		6,600,000	5,000,000
Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	607,636,000		607,636,000	576,321,000
Increase (Decrease) in loan portfolios			31,315,000
Net loan transfers from pass to substandard	21,000,000		21,000,000
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	74,113,000		74,113,000	54,687,000
Increase (Decrease) in loan portfolios			19,426,000
Net loan transfers from pass to substandard	21,000,000		21,000,000
Substandard | Construction loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				2,047,000
Increase (Decrease) in loan portfolios			(2,047,000)
Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	0		0	662,000
Increase (Decrease) in loan portfolios			(662,000)
Performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings	16,180,000		16,180,000
Number of loans added	7		7
Nonperforming
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (Decrease) in loan portfolios			1,100,000
Troubled debt restructurings	6,180,000		6,180,000	4,214,000
Number of loans added	6		6	1
Increase in troubled debt restructurings			2,000,000
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due loans	17,014,000		17,014,000	4,057,000
Increase of Loans past due for 90 days or more			2,800,000
Loans past due 90 days or more	4,775,000		4,775,000	2,021,000
30-59 Days Past Due	8,757,000		8,757,000	1,877,000
Nonaccrual loans	10,280,000		10,280,000	4,702,000
Fully collateralized unpaid loan, current	156,623,000		156,623,000	175,248,000
Gross loans	173,637,000		173,637,000	179,305,000
Loans, allowances	8,408,000	6,223,000	8,408,000	8,908,000	10,017,000
Total impaired loans	20,366,000		20,366,000	5,139,000
Investment in impaired loans			9,402,000	3,117,000
Commercial loans | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	135,717,000		135,717,000	149,522,000
Increase (Decrease) in loan portfolios			(13,805,000)
Commercial loans | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	27,670,000		27,670,000	24,551,000
Increase (Decrease) in loan portfolios			3,119,000
Commercial loans | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans				662,000
Increase (Decrease) in loan portfolios			(662,000)
Commercial loans | Performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings	9,280,000		9,280,000
Number of loans added	3		3
Commercial loans | Nonperforming
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings	2,045,000		2,045,000
Number of loans added	4		4
All other | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	4,071,000		4,071,000	4,214,000
Fully collateralized unpaid loan, current	155,118,000		155,118,000
Gross loans	155,118,000		155,118,000	121,813,000
Total impaired loans	9,542,000		9,542,000	4,310,000
Investment in impaired loans			8,528,000	12,701,000
All other | Pass | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	134,013,000		134,013,000	109,482,000
Increase (Decrease) in loan portfolios			24,531,000
All other | Substandard | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	17,218,000		17,218,000	9,778,000
Increase (Decrease) in loan portfolios			7,440,000
All other | Performing | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings	5,471,000		5,471,000
Number of loans added	3		3
All other | Nonperforming | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings	4,071,000		4,071,000	4,214,000
Number of loans added	1		1	1
Financing Receivables Impaired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, allowances	$ 4,200,000		$ 4,200,000	$ 2,800,000