Summary of significant accounting policies (Details 4) (Mortgage servicing assets, Bank, USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Mortgage servicing assets | Bank
Amortized intangible assets
Gross carrying amount	$ 21,171,000	$ 18,483,000
Accumulated amortization	(12,769,000)	(11,656,000)
Valuation allowance	(175,000)	(128,000)	(201,000)
Net carrying value	8,227,000	6,699,000
Changes in the valuation allowance for mortgage servicing assets
Valuation allowance, balance at the beginning of the period	128,000	201,000	268,000
Provision (recovery)	121,000	(12,000)	166,000
Other-than-temporary impairment	(74,000)	(61,000)	(233,000)
Valuation allowance, balance at the end of the period	175,000	128,000	201,000
Estimated aggregate amortization expenses
2012	1,300,000
2013	1,100,000
2014	900,000
2015	800,000
2016	700,000
Assets acquired through the sale or securitization of loans held for sale	2,800,000	3,300,000	3,300,000
Amortization Expenses	$ 1,100,000	$ 900,000	$ 800,000