Deferred Tax Assets and Income Taxes (Details) (USD $)	3 Months Ended			12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2010	Dec. 31, 2009
Deferred tax assets
Reserves for loan losses	$ 9,983,000			$ 14,348,000
Forgone interest on non-accrual loans	831,000			884,000
Fixed assets	481,000			405,000
Accruals	1,048,000			792,000
Alternative minimum tax credit	2,024,000			2,153,000
Deferred income	1,876,000			1,838,000
Deferred compensation	1,529,000			1,477,000
Net operating loss carryforward	189,000			907,000
Other than temporary impairment				45,000
Realized built-in loss subject to 382	2,685,000			3,234,000
Charitable contribution	61,000			61,000
State deferred tax	693,000			59,000
Total deferred tax assets	21,400,000			26,203,000
Deferred tax liabilities
Fair value adjustment for purchased assets	421,000			455,000
Investment securities valuation	1,069,000			2,745,000
Deferred costs, prepaids and FHLB advances	951,000			1,070,000
Total deferred tax liabilities	2,441,000			4,270,000
Net deferred tax assets	18,959,000			21,933,000
Cumulative loss position period					3 years	3 years
Change in deferred tax asset valuation allowance		(800,000)	(1,500,000)	(5,600,000)	7,100,000
Determination of the valuation allowance, cumulative pre-tax losses period					3 years
Determination of the valuation allowance, expected deferred tax assets realization period					5 years
Current:
Federal	(2,048,000)	(269,000)
State	(211,000)	(293,000)
Total current benefit	(2,259,000)	(562,000)
Deferred:
Federal	3,777,000	567,000
State	873,000	421,000
Total deferred expense	4,650,000	988,000
Deferred Tax Valuation Allowance
Federal		(592,000)
State		(208,000)
Total deferred tax valuation allowance change		(800,000)
Total income tax expense / (benefit)	2,391,000	(374,000)
Reconciliation of the statutory federal income tax expense / (benefit) to the Company's effective income tax expense / (benefit)
Tax expense at federal statutory tax rate	2,142,000	424,000
State income taxes, net of federal income tax benefit	430,000	83,000
Change in deferred tax asset valuation allowance		(800,000)
Bank owned life insurance	(44,000)	(18,000)
Tax exempt income, net of interest expense	(121,000)	(54,000)
Other, net	(16,000)	(9,000)
Total income tax expense / (benefit)	$ 2,391,000	$ (374,000)
Reconciliation of the statutory federal income tax expense / (benefit) rate to the Company's effective income tax expense / (benefit) rate
Tax expense at federal statutory tax rate (as a percent)	35.00%	35.00%
State income taxes, net of federal income tax benefit (as a percent)	7.00%	6.90%
Change in deferred tax asset valuation allowance (as a percent)	0.00%	(66.10%)
Bank owned life insurance (as a percent)	(0.70%)	(1.50%)
Tax exempt income, net of interest expense (as a percent)	(2.00%)	(4.40%)
Other, net (as a percent)	(0.20%)	(0.80%)
Total income tax expense/(benefit) (as a percent)	39.10%	(30.90%)