Loans (Details 5) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Impaired loans
Nonaccrual loans	$ 9,588,000	$ 9,967,000
Total impaired loans	18,386,000	19,369,000
Impaired loans, total legal contractual balances	24,300,000	24,900,000
Amount received in non-accrual interest	1,600,000	1,400,000
Impairment charges	4,300,000	4,100,000
Performing | Loans categorized as impaired
Impaired loans
Trouble debt restructuring	8,798,000	9,402,000
Nonaccrual | Loans categorized as impaired
Impaired loans
Trouble debt restructuring	$ 6,100,000	$ 6,500,000