Fair Value Measurement (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended			12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011		Dec. 31, 2011		Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity Securities, Fair Value		$ 94,921		$ 85,112
Aggregate fair value	17,540	39,340		30,077
Contractual balance	16,635	37,786		28,948
Gain	905	1,554	[1]	1,129	[1]
Financial assets:
Cash and due from banks, carrying value	238,417	318,945		377,319		523,113
Available for sale securities, carrying value	2,911,993	3,198,046		3,353,553
Held to maturity Securities	620,631	92,214		82,764
Other securities	140,730	160,793		140,726
Loans held for sale		39,340		30,077
Net noncovered loans	8,217,478	7,522,385		7,641,245
Net covered loans and loss share receivable	1,131,285	1,612,615		1,460,723
Accrued interest receivable	43,901	41,199		42,274
Derivatives	68,047	65,318		62,056
Financial liabilities:
Deposits	11,532,426	11,396,121		11,431,609
Total Federal funds purchased and securities sold under agreements to repurchase	963,455	987,030		866,265
Wholesale borrowings	178,083	248,006		203,462
Accrued interest payable	2,798	4,627		3,915
Derivatives	84,938	89,657		86,106
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity Securities, Fair Value	631,237	94,921		85,112
Financial assets:
Cash and due from banks, fair value	238,417	318,945		377,319
Available for sale securities, fair value	2,911,993	3,198,046		3,353,553
Other securities	140,730	160,793		140,726
Loans held for sale	17,540	39,340		30,077
Noncovered Loans and Leases Receivable Fair Value	7,898,195	7,148,775		7,373,801
Covered Loans and Leases Receivable Fair Value Disclosure	1,131,285	1,612,615		1,460,723
Accrued Interest Receivable Fair Value Disclosure	43,901	41,199		42,274
Derivatives	68,047	65,318		62,101
Financial liabilities:
Deposits	11,540,681	11,412,576		11,445,777
Total Federal funds purchased and securities sold under agreements to repurchase	963,455	991,304		866,265
Wholesale borrowings	187,230	256,069		211,623
Accrued interest payable	2,798	4,627		3,915
Derivatives	84,938	89,657		86,150
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity Securities, Fair Value	0	0		0
Financial assets:
Cash and due from banks, fair value	0	0		0
Available for sale securities, fair value	3,245	3,715		3,299
Other securities		0
Loans held for sale	0	0		0
Noncovered Loans and Leases Receivable Fair Value	0	0		0
Covered Loans and Leases Receivable Fair Value Disclosure	0	0		0
Accrued Interest Receivable Fair Value Disclosure	0	0		0
Derivatives	0	0		0
Financial liabilities:
Deposits		0
Total Federal funds purchased and securities sold under agreements to repurchase		0
Wholesale borrowings		0
Accrued interest payable		0
Derivatives	0	0		0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity Securities, Fair Value	631,237	94,921				85,112
Financial assets:
Cash and due from banks, fair value	238,417	318,945		377,319
Available for sale securities, fair value	2,861,244	3,103,290		3,262,715
Loans held for sale	17,540	39,340		30,077
Noncovered Loans and Leases Receivable Fair Value	0	0		0
Covered Loans and Leases Receivable Fair Value Disclosure	0	0		0
Accrued Interest Receivable Fair Value Disclosure	43,901	41,199		42,274
Derivatives	68,047	65,318		62,101
Financial liabilities:
Deposits	11,540,681	11,412,576		11,445,777
Total Federal funds purchased and securities sold under agreements to repurchase	963,455	991,304		866,265
Wholesale borrowings	187,230	256,069		211,623
Accrued interest payable	2,798	4,627		3,915
Derivatives	84,938	89,657		86,150
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity Securities, Fair Value	0	0		0
Financial assets:
Cash and due from banks, fair value	0	0		0
Available for sale securities, fair value	47,504	91,041		87,539
Other securities		0
Loans held for sale	0	0		0
Noncovered Loans and Leases Receivable Fair Value	7,898,195	7,148,775		7,373,801
Covered Loans and Leases Receivable Fair Value Disclosure	1,131,285	1,612,615		1,460,723
Accrued Interest Receivable Fair Value Disclosure	0	0		0
Derivatives	0	0		0
Financial liabilities:
Deposits		0
Total Federal funds purchased and securities sold under agreements to repurchase		0
Wholesale borrowings		0
Accrued interest payable		0
Derivatives	$ 0	$ 0		$ 0

[1] Included in loan sales and servicing income.