Allowance for loan losses (Details 4) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012 loans	Dec. 31, 2011 loans
Summary of Loans Modified as TDRS
Number of Loans	2,454,000	2,502,000
Recorded Investment	$ 158,000	$ 150,356
Unpaid Principal Balance	202,805	183,994
Summary of Loans Modified as TDRS Which Defaulted
Number of Loans	148,000
Recorded Investment	4,030
Noncovered Loans [Member]
Summary of Loans Modified as TDRS
Number of Loans	81,000	64,000
Recorded Investment	26,662	15,002
Unpaid Principal Balance	37,261	20,980
Summary of Loans Modified as TDRS Which Defaulted
Number of Loans	0
Recorded Investment	0
Noncovered Loans [Member] | Commercial and Industrial Financing Receivable [Member]
Summary of Loans Modified as TDRS
Number of Loans	19,000	14,000
Recorded Investment	4,074	2,512
Unpaid Principal Balance	10,584	4,336
Summary of Loans Modified as TDRS Which Defaulted
Number of Loans	0
Recorded Investment	0
Noncovered Loans [Member] | Commercial Real Estate [Member]
Summary of Loans Modified as TDRS
Number of Loans	35,000	28,000
Recorded Investment	18,618	9,167
Unpaid Principal Balance	22,135	12,659
Summary of Loans Modified as TDRS Which Defaulted
Number of Loans	0
Recorded Investment	0
Noncovered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Summary of Loans Modified as TDRS
Number of Loans	27,000	22,000
Recorded Investment	3,970	3,323
Unpaid Principal Balance	4,542	3,985
Summary of Loans Modified as TDRS Which Defaulted
Number of Loans	0
Recorded Investment	0
Noncovered Consumer Loans [Member]
Summary of Loans Modified as TDRS
Number of Loans	2,327,000	2,394,000
Recorded Investment	57,683	57,934
Unpaid Principal Balance	57,683	58,008
Summary of Loans Modified as TDRS Which Defaulted
Number of Loans	148,000
Recorded Investment	4,030
Noncovered Consumer Loans [Member] | Consumer Installment [Member]
Summary of Loans Modified as TDRS
Number of Loans	1,485,000	1,547,000
Recorded Investment	31,043	33,571
Unpaid Principal Balance	31,043	33,621
Summary of Loans Modified as TDRS Which Defaulted
Number of Loans	105,000
Recorded Investment	1,834
Noncovered Consumer Loans [Member] | Consumer Home Equity Lines Financing Receivable [Member]
Summary of Loans Modified as TDRS
Number of Loans	194,000	174,000
Recorded Investment	6,063	4,763
Unpaid Principal Balance	6,063	4,763
Noncovered Consumer Loans [Member] | Consumer Credit Card Financing Receivable [Member]
Summary of Loans Modified as TDRS
Number of Loans	461,000	496,000
Recorded Investment	1,998	2,202
Unpaid Principal Balance	1,998	2,202
Summary of Loans Modified as TDRS Which Defaulted
Number of Loans	14,000
Recorded Investment	88
Noncovered Consumer Loans [Member] | Consumer Residential Mortgages Financing Receivable [Member]
Summary of Loans Modified as TDRS
Number of Loans	187,000	177,000
Recorded Investment	18,579	17,398
Unpaid Principal Balance	18,579	17,422
Covered Loans [Member]
Summary of Loans Modified as TDRS
Number of Loans	46,000	44,000
Recorded Investment	73,655	77,420
Unpaid Principal Balance	107,861	105,006
Summary of Loans Modified as TDRS Which Defaulted
Number of Loans	0
Recorded Investment	0
Covered Loans [Member] | Commercial and Industrial Financing Receivable [Member]
Summary of Loans Modified as TDRS
Number of Loans	11,000	15,000
Recorded Investment	5,099	7,578
Unpaid Principal Balance	6,668	10,812
Summary of Loans Modified as TDRS Which Defaulted
Number of Loans	0
Recorded Investment	0
Covered Loans [Member] | Commercial Real Estate [Member]
Summary of Loans Modified as TDRS
Number of Loans	25,000	21,000
Recorded Investment	53,205	57,786
Unpaid Principal Balance	57,766	62,159
Summary of Loans Modified as TDRS Which Defaulted
Number of Loans	0
Recorded Investment	0
Covered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Summary of Loans Modified as TDRS
Number of Loans	10,000	8,000
Recorded Investment	15,351	12,056
Unpaid Principal Balance	43,427	32,035
Summary of Loans Modified as TDRS Which Defaulted
Number of Loans	0
Recorded Investment	$ 0