Bank subsidiary (Details 16) (USD $)	12 Months Ended
	Dec. 31, 2011 D	Dec. 31, 2010 D	Dec. 31, 2009 D
Securities sold under agreements to repurchase
Repurchase liability	$ 183,229,000
Weighted-average interest rate (as a percent)	1.56%
Fair value plus accrued interest	220,408,000
Amount outstanding as of end of the period	183,229,000
Weighted-average interest rate as of end of the period (as a percent)	1.56%
Advances from Federal Home Loan Bank
Thereafter	50,000,000
Total amount due	50,000,000
Weighted-average stated rate
Thereafter (as a percent)	4.28%
Total weighted-average stated rate (as a percent)	4.28%
Identical securities
Securities sold under agreements to repurchase
Repurchase liability	183,000,000	172,000,000	233,000,000
Weighted-average interest rate (as a percent)	1.56%	1.71%	1.38%
Amount outstanding as of end of the period	183,000,000	172,000,000	233,000,000
Average amount outstanding during the year	183,000,000	201,000,000	230,000,000
Maximum amount outstanding as of any month-end	186,000,000	238,000,000	241,000,000
Weighted-average interest rate as of end of the period (as a percent)	1.56%	1.71%	1.38%
Weighted-average interest rate during the year (as a percent)	1.61%	1.53%	1.55%
Weighted-average remaining days to maturity as of end of the period (in days)	490	628	544
Overnight
Securities sold under agreements to repurchase
Repurchase liability	132,932,000
Weighted-average interest rate (as a percent)	0.35%
Amount outstanding as of end of the period	132,932,000
Weighted-average interest rate as of end of the period (as a percent)	0.35%
Overnight | Collateralized by mortgage-related securities and federal agency obligations
Securities sold under agreements to repurchase
Fair value plus accrued interest	156,478,000
Over 90 days
Securities sold under agreements to repurchase
Repurchase liability	50,297,000
Weighted-average interest rate (as a percent)	4.75%
Amount outstanding as of end of the period	50,297,000
Weighted-average interest rate as of end of the period (as a percent)	4.75%
Over 90 days | Collateralized by mortgage-related securities and federal agency obligations
Securities sold under agreements to repurchase
Fair value plus accrued interest	$ 63,930,000