Allowance for loan losses (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	$ 121,282	$ 92,237	$ 111,610
Unpaid Principal Balance	139,889	120,611	138,970
Related Allowance	10,991	6,416	7,080
Average Recorded Investment	120,478	95,427	120,838
Total impaired loans with no related allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	47,828	43,379	48,331
Unpaid Principal Balance	60,302	63,033	73,802
Related Allowance	0	0	0
Average Recorded Investment	47,715	45,878	60,520
Total impaired loans with no related allowance [Member] | Commercial Loan [Member] | Commercial and Industrial Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	18,773	1,985	6,999
Unpaid Principal Balance	22,139	4,467	9,121
Related Allowance	0	0	0
Average Recorded Investment	16,455	2,513	8,442
Total impaired loans with no related allowance [Member] | Commercial Loan [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	20,426	31,986	29,566
Unpaid Principal Balance	26,942	43,575	46,744
Related Allowance	0	0	0
Average Recorded Investment	21,586	33,799	37,720
Total impaired loans with no related allowance [Member] | Commercial Loan [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	4,218	4,838	7,522
Unpaid Principal Balance	6,810	9,109	13,675
Related Allowance	0	0	0
Average Recorded Investment	4,956	4,919	9,908
Total impaired loans with no related allowance [Member] | Consumer Loan [Member] | Consumer Installment Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	0	0	0
Unpaid Principal Balance	0	0	0
Related Allowance	0	0	0
Average Recorded Investment	0	0	0
Total impaired loans with no related allowance [Member] | Consumer Loan [Member] | Consumer Home Equity Lines Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	0	0	0
Unpaid Principal Balance	0	0	0
Related Allowance	0	0	0
Average Recorded Investment	0	0	0
Total impaired loans with no related allowance [Member] | Consumer Loan [Member] | Consumer Credit Card Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	0	1,916	0
Unpaid Principal Balance	0	1,916	0
Related Allowance	0	0	0
Average Recorded Investment	0	1,974	0
Total impaired loans with no related allowance [Member] | Consumer Loan [Member] | Consumer Residential Mortgages Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	4,411	2,654	4,244
Unpaid Principal Balance	4,411	3,966	4,262
Related Allowance	0	0	0
Average Recorded Investment	4,718	2,673	4,450
Total impaired loans with a related allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	73,454	48,858	63,279
Unpaid Principal Balance	79,587	57,578	65,168
Related Allowance	10,991	6,416	7,080
Average Recorded Investment	72,763	49,549	60,318
Total impaired loans with a related allowance [Member] | Commercial Loan [Member] | Commercial and Industrial Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	6,477	1,588	1,270
Unpaid Principal Balance	10,511	2,010	1,769
Related Allowance	5,327	290	2,497
Average Recorded Investment	6,641	1,588	752
Total impaired loans with a related allowance [Member] | Commercial Loan [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	12,718	13,022	6,521
Unpaid Principal Balance	14,817	18,600	6,789
Related Allowance	1,977	3,169	1,599
Average Recorded Investment	11,007	13,566	3,247
Total impaired loans with a related allowance [Member] | Commercial Loan [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	987	4,569	1,798
Unpaid Principal Balance	987	7,181	2,864
Related Allowance	115	1,038	99
Average Recorded Investment	991	4,591	1,929
Total impaired loans with a related allowance [Member] | Consumer Loan [Member] | Consumer Installment Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	31,043	15,703	33,571
Unpaid Principal Balance	31,043	15,724	33,621
Related Allowance	1,773	662	1,382
Average Recorded Investment	31,581	15,794	33,742
Total impaired loans with a related allowance [Member] | Consumer Loan [Member] | Consumer Home Equity Lines Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	6,063	1,242	4,763
Unpaid Principal Balance	6,063	1,242	4,763
Related Allowance	22	20	31
Average Recorded Investment	6,192	1,256	4,996
Total impaired loans with a related allowance [Member] | Consumer Loan [Member] | Consumer Credit Card Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	1,998	537	2,202
Unpaid Principal Balance	1,998	537	2,202
Related Allowance	128	28	108
Average Recorded Investment	2,159	548	2,497
Total impaired loans with a related allowance [Member] | Consumer Loan [Member] | Consumer Residential Mortgages Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Recorded Investment	14,168	12,197	13,154
Unpaid Principal Balance	14,168	12,284	13,160
Related Allowance	1,649	1,209	1,364
Average Recorded Investment	$ 14,192	$ 12,206	$ 13,155