Allowance for loan losses (Details 1) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Mar. 31, 2011	Dec. 31, 2010
Legacy Loans
Total ending balance	$ 8,316,420
Commercial Portfolio Segment [Member]
Legacy Loans
Total ending balance	3,049,229
Commercial Real Estate Portfolio Segment [Member]
Legacy Loans
Total ending balance	2,153,342
Commercial Construction Financing Receivable Portfolio Segment [Member]
Legacy Loans
Total ending balance	309,105
Finance Leases Portfolio Segment [Member]
Legacy Loans
Total ending balance	110,938
Installment Financing Receivable Portfolio Segment [Member]
Legacy Loans
Total ending balance	1,321,082
Home Equity Receivable Portfolio Segment [Member]
Legacy Loans
Total ending balance	789,742
Credit Card Receivables Portfolio Segment [Member]
Legacy Loans
Total ending balance	143,919
Residential Portfolio Segment [Member]
Legacy Loans
Total ending balance	439,063
Noncovered Loans [Member]
Allowance for loan losses
Individually evaluated for impairment	8,444		7,080	6,671
Collectively evaluated for impairment	90,498		100,619	102,516
Financing Receivable, Allowance for Credit Losses	98,942	103,849	107,699	109,187	109,187	114,690
Legacy Loans
Ending Balance: Individually Evaluated	108,378
Ending Balance: Collectively Evaluated	8,208,042
Total ending balance			7,748,944	7,631,572
Noncovered Loans [Member] | Commercial Portfolio Segment [Member]
Allowance for loan losses
Individually evaluated for impairment	(2,900)		(2,497)	(256)
Collectively evaluated for impairment	(36,259)		(29,866)	(30,082)
Financing Receivable, Allowance for Credit Losses	39,159	40,327	32,363	30,338	28,366	29,764
Legacy Loans
Ending Balance: Individually Evaluated	9,994
Ending Balance: Collectively Evaluated	3,039,235
Noncovered Loans [Member] | Commercial Real Estate Portfolio Segment [Member]
Allowance for loan losses
Individually evaluated for impairment	1,953		1,599	2,064
Collectively evaluated for impairment	23,225		30,258	31,237
Financing Receivable, Allowance for Credit Losses	25,178	27,186	31,857	33,301	32,946	32,026
Legacy Loans
Ending Balance: Individually Evaluated	28,972
Ending Balance: Collectively Evaluated	2,124,370
Noncovered Loans [Member] | Commercial Construction Financing Receivable Portfolio Segment [Member]
Allowance for loan losses
Individually evaluated for impairment	117		99	1,264
Collectively evaluated for impairment	4,687		5,074	5,551
Financing Receivable, Allowance for Credit Losses	4,804	5,147	5,173	6,815	7,876	7,180
Legacy Loans
Ending Balance: Individually Evaluated	3,577
Ending Balance: Collectively Evaluated	305,528
Noncovered Loans [Member] | Finance Leases Portfolio Segment [Member]
Allowance for loan losses
Individually evaluated for impairment	0		0	0
Collectively evaluated for impairment	(506)		(341)	(325)
Financing Receivable, Allowance for Credit Losses	506	358	341	325	353	475
Legacy Loans
Ending Balance: Individually Evaluated	0
Ending Balance: Collectively Evaluated	110,938
Noncovered Loans [Member] | Installment Financing Receivable Portfolio Segment [Member]
Allowance for loan losses
Individually evaluated for impairment	1,674		1,382	1,568
Collectively evaluated for impairment	10,161		16,599	16,755
Financing Receivable, Allowance for Credit Losses	11,835	13,029	17,981	18,323	18,089	21,555
Legacy Loans
Ending Balance: Individually Evaluated	32,577
Ending Balance: Collectively Evaluated	1,288,505
Noncovered Loans [Member] | Home Equity Receivable Portfolio Segment [Member]
Allowance for loan losses
Individually evaluated for impairment	(95)		(31)	(52)
Collectively evaluated for impairment	(4,790)		(6,735)	(6,191)
Financing Receivable, Allowance for Credit Losses	4,885	5,449	6,766	6,243	7,142	7,217
Legacy Loans
Ending Balance: Individually Evaluated	6,922
Ending Balance: Collectively Evaluated	782,820
Noncovered Loans [Member] | Credit Card Receivables Portfolio Segment [Member]
Allowance for loan losses
Individually evaluated for impairment	106		108	121
Collectively evaluated for impairment	7,129		7,261	7,875
Financing Receivable, Allowance for Credit Losses	7,235	6,690	7,369	7,996	8,403	11,107
Legacy Loans
Ending Balance: Individually Evaluated	1,767
Ending Balance: Collectively Evaluated	142,152
Noncovered Loans [Member] | Residential Portfolio Segment [Member]
Allowance for loan losses
Individually evaluated for impairment	1,599		1,364	1,346
Collectively evaluated for impairment	3,741		4,485	4,500
Financing Receivable, Allowance for Credit Losses	5,340	5,663	5,849	5,846	6,012	5,366
Legacy Loans
Ending Balance: Individually Evaluated	24,569
Ending Balance: Collectively Evaluated	414,494
Legacy Loans [Member]
Legacy Loans
Ending Balance: Individually Evaluated			111,610	113,087
Ending Balance: Collectively Evaluated			7,637,334	7,518,485
Total ending balance	8,260,426		7,635,776	7,453,613
Legacy Loans [Member] | Commercial Portfolio Segment [Member]
Legacy Loans
Ending Balance: Individually Evaluated			8,269	4,271
Ending Balance: Collectively Evaluated			2,767,207	2,697,987
Total ending balance			2,775,476	2,702,258
Legacy Loans [Member] | Commercial Real Estate Portfolio Segment [Member]
Legacy Loans
Ending Balance: Individually Evaluated			36,087	39,288
Ending Balance: Collectively Evaluated			2,018,849	2,024,734
Total ending balance			2,054,936	2,064,022
Legacy Loans [Member] | Commercial Construction Financing Receivable Portfolio Segment [Member]
Legacy Loans
Ending Balance: Individually Evaluated			9,320	11,789
Ending Balance: Collectively Evaluated			268,015	240,788
Total ending balance			277,335	252,577
Legacy Loans [Member] | Finance Leases Portfolio Segment [Member]
Legacy Loans
Ending Balance: Individually Evaluated			0	0
Ending Balance: Collectively Evaluated			73,530	57,992
Total ending balance			73,530	57,992
Legacy Loans [Member] | Installment Financing Receivable Portfolio Segment [Member]
Legacy Loans
Ending Balance: Individually Evaluated			33,571	34,654
Ending Balance: Collectively Evaluated			1,230,094	1,236,673
Total ending balance			1,263,665	1,271,327
Legacy Loans [Member] | Home Equity Receivable Portfolio Segment [Member]
Legacy Loans
Ending Balance: Individually Evaluated			4,763	4,413
Ending Balance: Collectively Evaluated			739,219	738,964
Total ending balance			743,982	743,377
Legacy Loans [Member] | Credit Card Receivables Portfolio Segment [Member]
Legacy Loans
Ending Balance: Individually Evaluated			2,202	2,356
Ending Balance: Collectively Evaluated			144,154	140,354
Total ending balance			146,356	142,710
Legacy Loans [Member] | Residential Portfolio Segment [Member]
Legacy Loans
Ending Balance: Individually Evaluated			17,398	16,316
Ending Balance: Collectively Evaluated			396,266	380,993
Total ending balance			$ 413,664	$ 397,309