Loans and reserve for credit losses (Details Textual) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Mar. 31, 2013	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Increase (Decrease) in Finance Receivables	$ 54,400,000
Percentage Of Real Estate Related Loans	74.00%
Loans participated to third-parties	11,400,000	12,700,000
Impaired loans,Total recorded balance	51,732,000	68,671,000
Loans and Leases Receivable, Consumer, Allowance	22,694,000	27,261,000	24,548,000	38,219,000	43,951,000	43,905,000
Remaining Commitment To Lend Loan	0			1,300,000
Impaired Financing Receivable, Interest Income, Accrual Method	300,000	1,500,000
Customer Payoff Paydown Loans Restructure And Foreclosure Of Loans	11,300,000		57,200,000
Commercial Real Estate [Member]
Impaired loans,Total recorded balance	42,478,000	42,859,000
Loans and Leases Receivable, Consumer, Allowance	10,712,000	11,596,000	11,225,000	18,103,000	22,314,000	21,648,000
Troubled Debt Restructuring [Member]
Impaired loans,Total recorded balance	32,900,000	43,600,000
Loans and Leases Receivable, Consumer, Allowance	$ 1,800,000	$ 2,700,000