Fair Value Part 3 (Details) (USD $)	3 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]
Securities held to maturity	$ 52,010,000		$ 57,705,000
Net LHFI, excluding covered loans	5,683,874,000		5,767,966,000
Net acquired loans	174,315,000		76,302,000
FDIC indemnification asset	28,260,000		28,348,000	0
Deposits	8,090,746,000		7,566,363,000
Subordinated notes	49,847,000		49,839,000
Junior subordinated debt securities	61,856,000		61,856,000
Nonfinancial Assets and Liabilities [Abstract]
Foreclosed assets measured at fair value	8,900,000	19,600,000
Allowance for possible loan losses, Charge-offs	392,000	1,800,000
Foreclosed assets re-measured after initial recognition	13,200,000	8,700,000
Write-downs Of Allowance For Foreclosed Assets After Initial Recognition	2,400,000	2,000,000
Outstanding balances in impaired loans	60,900,000		68,900,000
Estimated fair value of financial instruments with immediate and shorter-term maturities maximum (in days)	90 days or less
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	219,801,000		211,883,000
Securities held to maturity	52,010,000		57,705,000
Deposits	8,090,746,000		7,566,363,000
Short-term liabilities	336,901,000		692,128,000
Subordinated notes	49,847,000		49,839,000
Junior subordinated debt securities	61,856,000		61,856,000
Fair Value, Inputs, Level 2 [Member] | 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]
Cash and short-term investments	219,801,000		211,883,000
Securities held to maturity	56,713,000		62,515,000
Deposits	8,099,675,000		7,575,064,000
Short-term liabilities	336,901,000		692,128,000
Subordinated notes	52,460,000		51,438,000
Junior subordinated debt securities	37,114,000		35,876,000
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net LHFI, excluding covered loans	5,683,874,000		5,767,966,000
Net acquired loans	174,315,000		76,302,000
FDIC indemnification asset	28,260,000		28,348,000
Fair Value, Inputs, Level 3 [Member] | 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]
Net LHFI, excluding covered loans	5,769,861,000		5,848,791,000
Net acquired loans	174,315,000		76,302,000
FDIC indemnification asset	$ 28,260,000		$ 28,348,000