Fair Value Information (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010	Dec. 31, 2009
Assets
Total cash and cash equivalents	$ 35,407		$ 67,279
Interest-earning balances due from depository institutions	0		50,227
FHLB Stock	72,689		86,744
Investment securities available-for-sale, at fair value (amortized cost of $2130029 at December 31,2011 and $1780493 at December 31,2010	2,201,526		1,791,558
Investment securities held-to-maturity	2,383		3,143
Loans held-for-sale			2,954
Covered loans held-for-sale	5,664
Accrued interest receivable	23,512		23,647
Deposits:
Noninterest-bearing	2,027,876		1,701,523
Interest-bearing	2,576,672		2,817,305
Junior subordinated debentures	115,055		115,055
Accrued interest payable	3,526		4,985
Non-covered loans held for sale activity [Member]
Assets
Loans held-for-sale	348		2,954	1,439
Covered loans held for sale activity [Member]
Assets
Loans held-for-sale	5,664	5,700	0	0
Covered loans held-for-sale	5,664
Estimated Fair Value [Member]
Assets
Total cash and cash equivalents	345,343		404,275
Interest-earning balances due from depository institutions	60,000		50,190
FHLB Stock	72,689		86,744
Investment securities available-for-sale, at fair value (amortized cost of $2130029 at December 31,2011 and $1780493 at December 31,2010	2,201,526		1,791,558
Investment securities held-to-maturity	2,383		3,143
Loans held-for-sale			2,954
Total Loans, net of allowance for credit losses	3,534,960		3,729,296
Accrued interest receivable	23,512		23,647
Interest Rate Swaps	20,497		9,127
Deposits:
Noninterest-bearing	2,027,876		1,701,523
Interest-bearing	2,577,825		2,818,390
Demand note to U.S. Treasury	0		1,917
Borrowings	1,012,211		1,128,562
Junior subordinated debentures	115,854		115,823
Accrued interest payable	3,526		4,985
Swaps	20,497		9,127
Estimated Fair Value [Member] | Non-covered loans held for sale activity [Member]
Assets
Loans held-for-sale	348
Estimated Fair Value [Member] | Covered loans held for sale activity [Member]
Assets
Covered loans held-for-sale	5,664
Carrying Amount [Member]
Assets
Total cash and cash equivalents	345,343		404,275
Interest-earning balances due from depository institutions	60,000		50,190
FHLB Stock	72,689		86,744
Investment securities available-for-sale, at fair value (amortized cost of $2130029 at December 31,2011 and $1780493 at December 31,2010	2,201,526		1,791,558
Investment securities held-to-maturity	2,383		3,143
Loans held-for-sale			2,954
Total Loans, net of allowance for credit losses	3,382,632		3,642,481
Accrued interest receivable	23,512		23,647
Interest Rate Swaps	20,497		9,127
Deposits:
Noninterest-bearing	2,027,876		1,701,523
Interest-bearing	2,576,672		2,817,305
Demand note to U.S. Treasury	0		1,917
Borrowings	958,032		1,095,578
Junior subordinated debentures	115,055		115,055
Accrued interest payable	3,526		4,985
Swaps	20,497		9,127
Carrying Amount [Member] | Non-covered loans held for sale activity [Member]
Assets
Loans held-for-sale	$ 348