Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Assets:
Cash and cash equivalents	$ 438,720	$ 381,940	$ 611,284	$ 536,165
Investment securities:
Loans held-for-sale	15,075	18,818	15,212
Net loans	3,934,465	3,742,952	3,671,713
Liabilities:
FHLB advances	37,237	43,057	45,991
Carrying Amount [Member]
Investment securities:
Available-for-sale	4,755	0	0
Nonmarketable equity securities	25,572	25,572	25,572
Carrying Amount [Member] \| Level 1[Member]
Assets:
Cash and cash equivalents	438,720	381,940	611,284
Carrying Amount [Member] \| Level 2 [Member]
Investment securities:
Available-for-sale	641,823	667,276	610,493
Held-to-maturity	213,536	175,339	178,432
Loans held-for-sale	15,075	18,818	15,212
Interest receivable	16,868	16,308	15,810
Liabilities:
Deposits without defined maturities	3,185,654	2,851,883	2,942,811
Interest payable	1,603	2,147	2,427
Short-term borrowings	311,471	303,786	302,298
FHLB advances	37,237	43,057	45,991
Carrying Amount [Member] \| Level 3 [Member]
Investment securities:
Held-to-maturity	8,000	8,000	8,000
Net loans	3,934,465	3,742,952	3,671,713
Liabilities:
Time deposits	1,413,218	1,514,974	1,537,775
Fair Value [Member]
Investment securities:
Available-for-sale	4,755	0	0
Nonmarketable equity securities	25,572	25,572	25,572
Fair Value [Member] \| Level 1[Member]
Assets:
Cash and cash equivalents	438,720	381,940	611,284
Fair Value [Member] \| Level 2 [Member]
Investment securities:
Available-for-sale	641,823	667,276	610,493
Held-to-maturity	215,185	175,769	177,024
Loans held-for-sale	15,075	18,972	15,212
Interest receivable	16,868	16,308	15,810
Liabilities:
Deposits without defined maturities	3,185,654	2,851,883	2,942,811
Interest payable	1,603	2,147	2,427
Short-term borrowings	311,471	303,786	302,298
FHLB advances	37,971	44,307	47,365
Fair Value [Member] \| Level 3 [Member]
Investment securities:
Held-to-maturity	8,000	8,000	8,000
Net loans	3,951,313	3,753,799	3,684,251
Liabilities:
Time deposits	$ 1,432,493	$ 1,538,566	$ 1,562,604

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