Bank subsidiary (Details 15) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Deposit liabilities
Savings	$ 1,684,875,000	$ 1,623,211,000
Other checking
Interest-bearing	610,542,000	589,228,000
Noninterest-bearing	538,214,000	473,297,000
Commercial checking	455,614,000	392,345,000
Money market	236,641,000	230,990,000
Term certificates	544,146,000	666,301,000
Total Amount	4,070,032,000	3,975,372,000
Weighted-average stated rate
Savings (as a percent)	0.07%	0.12%
Other checking, interest bearing (as a percent)	0.02%	0.05%
Money market (as a percent)	0.21%	0.28%
Term certificates (as a percent)	0.98%	1.25%
Total weighted-average stated rate (as a percent)	0.18%	0.28%
Certificate accounts of $100,000 or more	119,000,000	153,000,000
Term certificates outstanding, scheduled maturities
2012	325,000,000
2013	79,000,000
2014	45,000,000
2015	56,000,000
2016	26,000,000
Thereafter	13,000,000
Interest expense on deposit liabilities by type of deposit
Term certificates	6,393,000	11,221,000	27,369,000
Savings	1,756,000	2,262,000	4,952,000
Money market	650,000	884,000	886,000
Interest-bearing checking	184,000	329,000	839,000
Interest expense on deposit liabilities	$ 8,983,000	$ 14,696,000	$ 34,046,000