Allowance for loan losses Troubled debt restructuring (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Jun. 30, 2012	Dec. 31, 2011		Sep. 30, 2011		Mar. 31, 2011	Dec. 31, 2010
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	$ 166,327			$ 150,356		$ 129,979
Noncovered Loans [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	23,753			15,002		12,607
Financing Receivable, Allowance for Credit Losses	98,942		103,849	107,699		109,187		109,187	114,690
Noncovered Loans [Member] | Commercial and Industrial Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	2,413			2,512		1,096
Noncovered Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	17,763			9,167		8,068
Noncovered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	3,577			3,323		3,443
Noncovered Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	65,835			57,934		57,742
Noncovered Consumer Loans [Member] | Consumer Installment [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	32,577			33,571		34,654
Noncovered Consumer Loans [Member] | Consumer Home Equity Lines Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	6,922			4,763		4,413
Noncovered Consumer Loans [Member] | Consumer Credit Card Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	1,767			2,202		2,359
Noncovered Consumer Loans [Member] | Consumer Residential Mortgages Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	24,569			17,398		16,316
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	732,470	[1]		954,689	[2]	1,061,263	[3]
Financing Receivable, Recorded Investment, Past Due	310,588	[1]		336,787	[2]	365,484	[3]
Financing Receivable, Modifications, Recorded Investment	71,997			77,420		59,630
Covered Loans [Member] | Commercial and Industrial Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	5,278			7,578		7,287
Covered Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	52,080			57,786		41,403
Covered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	14,639			12,056		10,940
Covered Loans [Member] | Consumer Home Equity Lines Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Recorded Investment	4,742
Accruing TDRs [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	92,430			100,358		117,343
Financing Receivable, Recorded Investment, Past Due	54,573			38,245		5,263
Financing Receivable, Modifications, Recorded Investment	147,003			138,603		122,606
Accruing TDRs [Member] | Noncovered Loans [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	16,071			6,178		7,667
Financing Receivable, Recorded Investment, Past Due	2,464			513		0
Financing Receivable, Modifications, Recorded Investment	18,535			6,691		7,667
Accruing TDRs [Member] | Noncovered Loans [Member] | Commercial and Industrial Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	955			91		129
Financing Receivable, Recorded Investment, Past Due	0			0		0
Financing Receivable, Modifications, Recorded Investment	955			91		129
Accruing TDRs [Member] | Noncovered Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	11,609			3,305		4,778
Financing Receivable, Recorded Investment, Past Due	2,464			513		0
Financing Receivable, Modifications, Recorded Investment	14,073			3,818		4,778
Accruing TDRs [Member] | Noncovered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	3,507			2,782		2,760
Financing Receivable, Recorded Investment, Past Due	0			0		0
Financing Receivable, Modifications, Recorded Investment	3,507			2,782		2,760
Accruing TDRs [Member] | Noncovered Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	47,039			51,672		51,281
Financing Receivable, Recorded Investment, Past Due	4,690			2,820		4,028
Financing Receivable, Modifications, Recorded Investment	51,729			54,492		55,309
Accruing TDRs [Member] | Noncovered Consumer Loans [Member] | Consumer Installment [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	28,604			31,637		32,882
Financing Receivable, Recorded Investment, Past Due	1,071			1,800		1,772
Financing Receivable, Modifications, Recorded Investment	29,675			33,437		34,654
Accruing TDRs [Member] | Noncovered Consumer Loans [Member] | Consumer Home Equity Lines Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	5,394			4,226		3,885
Financing Receivable, Recorded Investment, Past Due	171			222		528
Financing Receivable, Modifications, Recorded Investment	5,565			4,448		4,413
Accruing TDRs [Member] | Noncovered Consumer Loans [Member] | Consumer Credit Card Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	1,655			2,073		2,201
Financing Receivable, Recorded Investment, Past Due	109			110		158
Financing Receivable, Modifications, Recorded Investment	1,764			2,183		2,359
Accruing TDRs [Member] | Noncovered Consumer Loans [Member] | Consumer Residential Mortgages Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	11,386			13,736		12,313
Financing Receivable, Recorded Investment, Past Due	3,339			688		1,570
Financing Receivable, Modifications, Recorded Investment	14,725			14,424		13,883
Accruing TDRs [Member] | Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	24,622			42,508		58,395
Financing Receivable, Recorded Investment, Past Due	47,375			34,912		1,235
Financing Receivable, Modifications, Recorded Investment	71,997			77,420		59,630
Accruing TDRs [Member] | Covered Loans [Member] | Commercial and Industrial Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	1,000			1,587		6,052
Financing Receivable, Recorded Investment, Past Due	4,278			5,991		1,235
Financing Receivable, Modifications, Recorded Investment	5,278			7,578		7,287
Accruing TDRs [Member] | Covered Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	17,298			35,083		41,403
Financing Receivable, Recorded Investment, Past Due	34,782			22,703		0
Financing Receivable, Modifications, Recorded Investment	52,080			57,786		41,403
Accruing TDRs [Member] | Covered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	6,324			5,838		10,940
Financing Receivable, Recorded Investment, Past Due	8,315			6,218		0
Financing Receivable, Modifications, Recorded Investment	14,639			12,056		10,940
Accruing TDRs [Member] | Covered Loans [Member] | Consumer Home Equity Lines Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	4,698
Financing Receivable, Recorded Investment, Past Due	44
Financing Receivable, Modifications, Recorded Investment	4,742
Nonaccruing TDRs [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	12,032			5,592		2,880
Financing Receivable, Recorded Investment, Past Due	7,292			6,161		4,493
Financing Receivable, Modifications, Recorded Investment	19,324			11,753		7,373
Nonaccruing TDRs [Member] | Noncovered Loans [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	1,408			3,894		1,395
Financing Receivable, Recorded Investment, Past Due	3,810			4,417		3,545
Financing Receivable, Modifications, Recorded Investment	5,218			8,311		4,940
Nonaccruing TDRs [Member] | Noncovered Loans [Member] | Commercial and Industrial Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	865			0		0
Financing Receivable, Recorded Investment, Past Due	593			2,421		967
Financing Receivable, Modifications, Recorded Investment	1,458			2,421		967
Nonaccruing TDRs [Member] | Noncovered Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	473			3,590		1,215
Financing Receivable, Recorded Investment, Past Due	3,217			1,759		2,075
Financing Receivable, Modifications, Recorded Investment	3,690			5,349		3,290
Nonaccruing TDRs [Member] | Noncovered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	70			304		180
Financing Receivable, Recorded Investment, Past Due	0			237		503
Financing Receivable, Modifications, Recorded Investment	70			541		683
Nonaccruing TDRs [Member] | Noncovered Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	10,624			1,698		1,485
Financing Receivable, Recorded Investment, Past Due	3,482			1,744		948
Financing Receivable, Modifications, Recorded Investment	14,106			3,442		2,433
Nonaccruing TDRs [Member] | Noncovered Consumer Loans [Member] | Consumer Installment [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	2,882			0		0
Financing Receivable, Recorded Investment, Past Due	20			134		0
Financing Receivable, Modifications, Recorded Investment	2,902			134		0
Nonaccruing TDRs [Member] | Noncovered Consumer Loans [Member] | Consumer Home Equity Lines Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	1,131			76		0
Financing Receivable, Recorded Investment, Past Due	226			239		0
Financing Receivable, Modifications, Recorded Investment	1,357			315		0
Nonaccruing TDRs [Member] | Noncovered Consumer Loans [Member] | Consumer Credit Card Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	0			0		0
Financing Receivable, Recorded Investment, Past Due	3			19		0
Financing Receivable, Modifications, Recorded Investment	3			19		0
Nonaccruing TDRs [Member] | Noncovered Consumer Loans [Member] | Consumer Residential Mortgages Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	6,611			1,622		1,485
Financing Receivable, Recorded Investment, Past Due	3,233			1,352		948
Financing Receivable, Modifications, Recorded Investment	9,844			2,974		2,433
Nonaccruing TDRs [Member] | Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	0			0		0
Financing Receivable, Recorded Investment, Past Due	0			0		0
Financing Receivable, Modifications, Recorded Investment	0			0		0
Nonaccruing TDRs [Member] | Covered Loans [Member] | Commercial and Industrial Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	0			0		0
Financing Receivable, Recorded Investment, Past Due	0			0		0
Financing Receivable, Modifications, Recorded Investment	0			0		0
Nonaccruing TDRs [Member] | Covered Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	0			0		0
Financing Receivable, Recorded Investment, Past Due	0			0		0
Financing Receivable, Modifications, Recorded Investment	0			0		0
Nonaccruing TDRs [Member] | Covered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	0			0		0
Financing Receivable, Recorded Investment, Past Due	0			0		0
Financing Receivable, Modifications, Recorded Investment	0			0		0
Nonaccruing TDRs [Member] | Covered Loans [Member] | Consumer Home Equity Lines Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Recorded Investment, Current	0
Financing Receivable, Recorded Investment, Past Due	0
Financing Receivable, Modifications, Recorded Investment	0
Total Tdr Allowance [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	15,365			12,114		6,881
Total Tdr Allowance [Member] | Noncovered Loans [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	644			582		1,112
Total Tdr Allowance [Member] | Noncovered Loans [Member] | Commercial and Industrial Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	126			247		215
Total Tdr Allowance [Member] | Noncovered Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	401			236		125
Total Tdr Allowance [Member] | Noncovered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	117			99		772
Total Tdr Allowance [Member] | Noncovered Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	3,474			2,885		3,087
Total Tdr Allowance [Member] | Noncovered Consumer Loans [Member] | Consumer Installment [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	1,674			1,382		1,568
Total Tdr Allowance [Member] | Noncovered Consumer Loans [Member] | Consumer Home Equity Lines Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	95			31		52
Total Tdr Allowance [Member] | Noncovered Consumer Loans [Member] | Consumer Credit Card Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	106			108		121
Total Tdr Allowance [Member] | Noncovered Consumer Loans [Member] | Consumer Residential Mortgages Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	1,599			1,364		1,346
Total Tdr Allowance [Member] | Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	11,247			8,647		2,682
Total Tdr Allowance [Member] | Covered Loans [Member] | Commercial and Industrial Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	1,527			1,384		746
Total Tdr Allowance [Member] | Covered Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	8,088			6,567		1,542
Total Tdr Allowance [Member] | Covered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	1,632			696		394
Total Tdr Allowance [Member] | Covered Loans [Member] | Consumer Home Equity Lines Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Allowance for Credit Losses	$ 0

[1] Excludes loss share receivable of $131.9 million as of September 30, 2012.

[2] Excludes loss share receivable of $205.7 million as of December 31, 2011.

[3] Excludes loss share receivable of $220.5 million as of September 30, 2011