Allowance for loan losses (Details 5) (USD $)	Mar. 31, 2012		Dec. 31, 2011		Mar. 31, 2011		Dec. 31, 2010
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	$ 151,326,000		$ 150,356,000
Accruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	78,158,000		71,933,000
Delinquent	2,091,000		3,354,000
Total	80,249,000		75,287,000
Nonaccruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	33,414,000		33,986,000
Delinquent	37,663,000		41,083,000
Total	71,077,000		75,069,000
Total Tdr Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance	15,182,000		12,114,000
Noncovered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	17,117,000		15,002,000
Total Allowance	103,849,000		107,699,000		114,690,000		114,690,000
Noncovered Loans [Member] | Accruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	9,540,000		6,178,000
Delinquent	510,000		513,000
Total	10,050,000		6,691,000
Noncovered Loans [Member] | Nonaccruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	3,289,000		3,894,000
Delinquent	3,778,000		4,417,000
Total	7,067,000		8,311,000
Noncovered Loans [Member] | Total Tdr Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance	1,270,000		582,000
Noncovered Loans [Member] | Commercial and Industrial Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	3,388,000		2,512,000
Noncovered Loans [Member] | Commercial and Industrial Financing Receivable [Member] | Accruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	1,791,000		91,000
Delinquent	0		0
Total	1,791,000		91,000
Noncovered Loans [Member] | Commercial and Industrial Financing Receivable [Member] | Nonaccruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	0		0
Delinquent	1,597,000		2,421,000
Total	1,597,000		2,421,000
Noncovered Loans [Member] | Commercial and Industrial Financing Receivable [Member] | Total Tdr Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance	822,000		247,000
Noncovered Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	9,136,000		9,167,000
Noncovered Loans [Member] | Commercial Real Estate [Member] | Accruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	3,672,000		3,305,000
Delinquent	510,000		513,000
Total	4,182,000		3,818,000
Noncovered Loans [Member] | Commercial Real Estate [Member] | Nonaccruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	3,152,000		3,590,000
Delinquent	1,802,000		1,759,000
Total	4,954,000		5,349,000
Noncovered Loans [Member] | Commercial Real Estate [Member] | Total Tdr Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance	224,000		236,000
Noncovered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	4,593,000		3,323,000
Noncovered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member] | Accruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	4,077,000		2,782,000
Delinquent	0		0
Total	4,077,000		2,782,000
Noncovered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member] | Nonaccruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	137,000		304,000
Delinquent	379,000		237,000
Total	516,000		541,000
Noncovered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member] | Total Tdr Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance	224,000		99,000
Noncovered Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	58,036,000		57,934,000
Noncovered Consumer Loans [Member] | Accruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	53,091,000		51,628,000
Delinquent	1,581,000		2,841,000
Total	54,672,000		54,469,000
Noncovered Consumer Loans [Member] | Nonaccruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	2,993,000		1,711,000
Delinquent	371,000		1,754,000
Total	3,364,000		3,465,000
Noncovered Consumer Loans [Member] | Total Tdr Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance	3,563,000		2,885,000
Noncovered Consumer Loans [Member] | Consumer Installment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	32,378,000		33,571,000
Noncovered Consumer Loans [Member] | Consumer Installment [Member] | Accruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	31,167,000		31,635,000
Delinquent	1,134,000		1,802,000
Total	32,301,000		33,437,000
Noncovered Consumer Loans [Member] | Consumer Installment [Member] | Nonaccruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	0		0
Delinquent	77,000		134,000
Total	77,000		134,000
Noncovered Consumer Loans [Member] | Consumer Installment [Member] | Total Tdr Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance	1,901,000		1,382,000
Noncovered Consumer Loans [Member] | Consumer Home Equity Lines Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	5,522,000		4,763,000
Noncovered Consumer Loans [Member] | Consumer Home Equity Lines Financing Receivable [Member] | Accruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	4,828,000		4,226,000
Delinquent	387,000		222,000
Total	5,215,000		4,448,000
Noncovered Consumer Loans [Member] | Consumer Home Equity Lines Financing Receivable [Member] | Nonaccruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	75,000		76,000
Delinquent	232,000		239,000
Total	307,000		315,000
Noncovered Consumer Loans [Member] | Consumer Home Equity Lines Financing Receivable [Member] | Total Tdr Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance	66,000		31,000
Noncovered Consumer Loans [Member] | Consumer Credit Card Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	2,060,000		2,202,000
Noncovered Consumer Loans [Member] | Consumer Credit Card Financing Receivable [Member] | Accruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	1,997,000		2,073,000
Delinquent	60,000		110,000
Total	2,057,000		2,183,000
Noncovered Consumer Loans [Member] | Consumer Credit Card Financing Receivable [Member] | Nonaccruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	0		0
Delinquent	3,000		19,000
Total	3,000		19,000
Noncovered Consumer Loans [Member] | Consumer Credit Card Financing Receivable [Member] | Total Tdr Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance	92,000		108,000
Noncovered Consumer Loans [Member] | Consumer Residential Mortgages Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	18,076,000		17,398,000
Noncovered Consumer Loans [Member] | Consumer Residential Mortgages Financing Receivable [Member] | Accruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	15,099,000		13,694,000
Delinquent	0		707,000
Total	15,099,000		14,401,000
Noncovered Consumer Loans [Member] | Consumer Residential Mortgages Financing Receivable [Member] | Nonaccruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	2,918,000		1,635,000
Delinquent	59,000		1,362,000
Total	2,977,000		2,997,000
Noncovered Consumer Loans [Member] | Consumer Residential Mortgages Financing Receivable [Member] | Total Tdr Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance	1,504,000		1,364,000
Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	876,547,000	[1]	954,689,000	[2]	1,157,262,000	[3]
Delinquent	330,467,000	[1]	336,787,000	[2]	447,012,000	[3]
Total	76,173,000		77,420,000
Covered Loans [Member] | Accruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	15,527,000		14,127,000
Delinquent	0		0
Total	15,527,000		14,127,000
Covered Loans [Member] | Nonaccruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	27,132,000		28,381,000
Delinquent	33,514,000		34,912,000
Total	60,646,000		63,293,000
Covered Loans [Member] | Total Tdr Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance	10,349,000		8,647,000
Covered Loans [Member] | Commercial and Industrial Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	7,662,000		7,578,000
Covered Loans [Member] | Commercial and Industrial Financing Receivable [Member] | Accruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	855,000		565,000
Delinquent	0		0
Total	855,000		565,000
Covered Loans [Member] | Commercial and Industrial Financing Receivable [Member] | Nonaccruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	1,550,000		1,022,000
Delinquent	5,257,000		5,991,000
Total	6,807,000		7,013,000
Covered Loans [Member] | Commercial and Industrial Financing Receivable [Member] | Total Tdr Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance	1,384,000		1,384,000
Covered Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	54,824,000		57,786,000
Covered Loans [Member] | Commercial Real Estate [Member] | Accruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	14,672,000		13,562,000
Delinquent	0		0
Total	14,672,000		13,562,000
Covered Loans [Member] | Commercial Real Estate [Member] | Nonaccruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	21,747,000		21,521,000
Delinquent	18,405,000		22,703,000
Total	40,152,000		44,224,000
Covered Loans [Member] | Commercial Real Estate [Member] | Total Tdr Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance	7,720,000		6,567,000
Covered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	13,687,000		12,056,000
Covered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member] | Accruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	0		0
Delinquent	0		0
Total	0		0
Covered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member] | Nonaccruing TDRs [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current	3,835,000		5,838,000
Delinquent	9,852,000		6,218,000
Total	13,687,000		12,056,000
Covered Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member] | Total Tdr Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance	$ 1,245,000		$ 696,000

[1] Excludes loss share receivable of $171.1 million as of March 31, 2012.

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

[3] Excludes loss share receivable of $266.0 million as of March 31, 2011