Allowance for loan losses (Details 3) (USD $) In Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2011	Dec. 31, 2010
Summary of impaired noncovered loans
Recorded Investment	$ 92,237	$ 128,343
Unpaid Principal Balance	120,611	154,097
Related Allowance	6,416	6,181
Average Recorded Investment	95,429	134,730
Loans With Related Allowance [Member] | Commercial and Industrial [Member]
Summary of impaired noncovered loans
Recorded Investment	1,588	0
Unpaid Principal Balance	2,010	0
Related Allowance	290	0
Average Recorded Investment	1,588	0
Loans With Related Allowance [Member] | Commercial Real Estate [Member]
Summary of impaired noncovered loans
Recorded Investment	13,022	30,792
Unpaid Principal Balance	18,600	37,767
Related Allowance	3,169	3,852
Average Recorded Investment	13,566	33,172
Loans With Related Allowance [Member] | Construction [Member]
Summary of impaired noncovered loans
Recorded Investment	4,569	7,585
Unpaid Principal Balance	7,181	11,423
Related Allowance	1,038	1,588
Average Recorded Investment	4,591	8,928
Loans With Related Allowance [Member] | Installment [Member]
Summary of impaired noncovered loans
Recorded Investment	15,703	0
Unpaid Principal Balance	15,724	0
Related Allowance	662	0
Average Recorded Investment	15,794	0
Loans With Related Allowance [Member] | Consumer Home Equity Lines [Member]
Summary of impaired noncovered loans
Recorded Investment	1,242	0
Unpaid Principal Balance	1,242	0
Related Allowance	20	0
Average Recorded Investment	1,256	0
Loans With Related Allowance [Member] | Credit cards [Member]
Summary of impaired noncovered loans
Recorded Investment	2,453	0
Unpaid Principal Balance	2,453	0
Related Allowance	28	0
Average Recorded Investment	2,524	0
Loans With Related Allowance [Member] | Consumer Residential Mortgages [Member]
Summary of impaired noncovered loans
Recorded Investment	12,197	9,705
Unpaid Principal Balance	12,284	9,776
Related Allowance	1,209	741
Average Recorded Investment	12,206	9,713
Loans With No Related Allowance [Member] | Commercial and Industrial [Member]
Summary of impaired noncovered loans
Recorded Investment	1,985	12,172
Unpaid Principal Balance	4,467	15,045
Related Allowance	0	0
Average Recorded Investment	2,513	12,816
Loans With No Related Allowance [Member] | Commercial Real Estate [Member]
Summary of impaired noncovered loans
Recorded Investment	31,986	34,003
Unpaid Principal Balance	43,575	40,619
Related Allowance	0	0
Average Recorded Investment	33,799	35,238
Loans With No Related Allowance [Member] | Construction [Member]
Summary of impaired noncovered loans
Recorded Investment	4,838	10,120
Unpaid Principal Balance	9,109	14,710
Related Allowance	0	0
Average Recorded Investment	4,919	10,833
Loans With No Related Allowance [Member] | Installment [Member]
Summary of impaired noncovered loans
Recorded Investment	0	17,146
Unpaid Principal Balance	0	17,164
Related Allowance	0	0
Average Recorded Investment	0	17,313
Loans With No Related Allowance [Member] | Consumer Home Equity Lines [Member]
Summary of impaired noncovered loans
Recorded Investment	0	1,747
Unpaid Principal Balance	0	1,747
Related Allowance	0	0
Average Recorded Investment	0	1,764
Loans With No Related Allowance [Member] | Credit cards [Member]
Summary of impaired noncovered loans
Recorded Investment	0	3,081
Unpaid Principal Balance	0	3,081
Related Allowance	0	0
Average Recorded Investment	0	2,926
Loans With No Related Allowance [Member] | Consumer Residential Mortgages [Member]
Summary of impaired noncovered loans
Recorded Investment	2,654	1,992
Unpaid Principal Balance	3,966	2,765
Related Allowance	0	0
Average Recorded Investment	2,673	2,027
Commercial [Member]
Summary of impaired noncovered loans
Recorded Investment	57,988	94,672
Unpaid Principal Balance	84,942	119,564
Related Allowance	4,497	5,440
Average Recorded Investment	60,976	100,987
Consumer [Member]
Summary of impaired noncovered loans
Recorded Investment	34,249	33,671
Unpaid Principal Balance	35,669	34,533
Related Allowance	1,919	741
Average Recorded Investment	$ 34,453	$ 33,743