Fair Value Measurements (Schedule of Carrying Amounts and Estimated Fair Value of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Investment securities:
Available-for-sale	$ 705,146	$ 586,809	$ 646,578
Held-to-maturity	275,866	229,922	223,185
Carrying Amount [Member]
Investment securities:
Available-for-sale	0	4,755	4,755
Nonmarketable equity securities	25,572	25,572	25,572
Carrying Amount [Member] | Level 1[Member]
Assets:
Cash and cash equivalents	493,110	656,135	438,720
Carrying Amount [Member] | Level 2 [Member]
Investment securities:
Available-for-sale	705,146	582,054	641,823
Held-to-maturity	272,079	229,977	213,536
Loans Held-for-sale	7,907	17,665	15,075
Interest receivable	16,359	14,933	16,868
Liabilities:
Deposits without defined maturities	3,842,148	3,448,886	3,185,654
Interest payable	1,009	1,501	1,603
Short-term borrowings	357,595	310,463	311,471
FHLB advances	0	34,289	37,237
Carrying Amount [Member] | Level 3 [Member]
Investment securities:
Held-to-maturity	10,500	0	8,000
Net loans	4,441,139	4,083,244	3,934,465
Liabilities:
Time deposits	1,349,157	1,472,557	1,413,218
Fair Value [Member]
Investment securities:
Available-for-sale	0	4,755	4,755
Nonmarketable equity securities	25,572	25,572	25,572
Fair Value [Member] | Level 1[Member]
Assets:
Cash and cash equivalents	493,110	656,135	438,720
Fair Value [Member] | Level 2 [Member]
Investment securities:
Available-for-sale	705,146	582,054	641,823
Held-to-maturity	269,616	229,922	215,185
Loans Held-for-sale	7,907	17,665	15,075
Interest receivable	16,359	14,933	16,868
Liabilities:
Deposits without defined maturities	3,842,148	3,448,886	3,185,654
Interest payable	1,009	1,501	1,603
Short-term borrowings	357,595	310,463	311,471
FHLB advances	0	34,835	37,971
Fair Value [Member] | Level 3 [Member]
Investment securities:
Held-to-maturity	6,250	0	8,000
Net loans	4,446,796	4,093,880	3,951,313
Liabilities:
Time deposits	$ 1,359,739	$ 1,489,072	$ 1,432,493