Fair Value Measurement (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2012		Mar. 31, 2011		Dec. 31, 2011		Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate fair value	$ 42,447		$ 13,443		$ 30,077
Contractual balance	41,542		13,008		28,948
Gain	905	[1]	434	[1]	1,129	[1]
Financial assets:
Cash and due from banks, carrying value	489,985		638,781		377,319		523,113
Available for sale securities, carrying value	3,491,647		3,362,751		3,353,553		3,353,553
Available for sale securities, fair value			3,362,751		3,353,553
Held to maturity Securities	100,840		65,923		82,764
Other securities	140,713		160,818		140,726
Loans held for sale	42,447		13,443		30,077
Net noncovered loans	7,759,360		7,071,534		7,641,245
Net covered loans and loss share receivable	1,337,080		1,841,850		1,460,723
Accrued interest receivable	45,270		41,418		42,274
Derivatives	60,115		40,380		62,056
Financial liabilities:
Deposits	11,648,165		11,395,946		11,431,609
Total Federal funds purchased and securities sold under agreements to repurchase	928,760		952,995		866,265
Wholesale borrowings	176,611		325,046		203,462
Accrued interest payable	3,350		5,834		3,915
Derivatives	80,174		63,923		86,106
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial assets:
Cash and due from banks, carrying value			638,781		377,319
Cash and due from banks, fair value	489,985
Available for sale securities, fair value	3,491,647		3,362,751		3,353,553
Held to maturity Securities	103,865		67,903		85,112
Other securities	140,713		160,818		140,726
Loans held for sale	42,447		13,443		30,077
Net noncovered loans	7,496,821		6,673,608		7,373,801
Net covered loans and loss share receivable	1,337,080		1,841,850		1,460,723
Accrued interest receivable	45,270		41,418		42,274
Derivatives	60,115		40,380		62,056
Financial liabilities:
Deposits	11,659,976		11,416,463		11,445,777
Total Federal funds purchased and securities sold under agreements to repurchase	928,760		956,975		866,265
Wholesale borrowings	184,640		328,006		211,623
Accrued interest payable	3,350		5,834		3,915
Derivatives	80,174		63,923		86,106
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Financial assets:
Available for sale securities, fair value	3,308		3,839		3,299
Loans held for sale	0		0		0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Financial assets:
Cash and due from banks, carrying value			638,781		377,319
Cash and due from banks, fair value	489,985
Available for sale securities, fair value	3,399,852		3,231,998		3,262,715
Held to maturity Securities	103,865		67,903				85,112
Loans held for sale	42,447		13,443		30,077
Accrued interest receivable	45,270		41,418		42,274
Derivatives	60,115		40,380		62,056
Financial liabilities:
Deposits	11,659,976		11,416,463		11,445,777
Total Federal funds purchased and securities sold under agreements to repurchase	928,760		956,975		866,265
Wholesale borrowings	184,640		328,006		211,623
Accrued interest payable	3,350		5,834		3,915
Derivatives	80,174		63,923		86,106
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Financial assets:
Available for sale securities, fair value	88,487		126,914		87,539
Loans held for sale	0		0		0
Net noncovered loans	7,496,821		6,673,608		7,373,801
Net covered loans and loss share receivable	$ 1,337,080		$ 1,841,850		$ 1,460,723

[1] Included in loan sales and servicing income.