Fair Value Measurements (Schedule of Carrying Amounts and Estimated Fair Value of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
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	206,957	656,135	241,823
Carrying Amount [Member] | Level 2 [Member]
Investment securities:
Available-for-sale	734,052	582,054	675,476
Held-to-maturity	264,215	229,977	205,034
Loans Held-for-sale	9,180	17,665	12,625
Interest receivable	15,844	14,933	15,764
Liabilities:
Deposits without defined maturities	3,434,266	3,448,886	2,933,079
Interest payable	1,085	1,501	1,755
Short-term borrowings	346,995	310,463	299,748
FHLB advances	0	34,289	38,177
Carrying Amount [Member] | Level 3 [Member]
Investment securities:
Held-to-maturity	10,500	0	8,000
Net loans	4,253,687	4,083,244	3,875,631
Liabilities:
Time deposits	1,379,919	1,472,557	1,450,465
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	206,957	656,135	241,823
Fair Value [Member] | Level 2 [Member]
Investment securities:
Available-for-sale	734,052	582,054	675,476
Held-to-maturity	265,147	229,922	205,852
Loans Held-for-sale	9,180	17,665	12,625
Interest receivable	15,844	14,933	15,764
Liabilities:
Deposits without defined maturities	3,434,266	3,448,886	2,933,079
Interest payable	1,085	1,501	1,755
Short-term borrowings	346,995	310,463	299,748
FHLB advances	0	34,835	39,066
Fair Value [Member] | Level 3 [Member]
Investment securities:
Held-to-maturity	6,250	0	8,000
Net loans	4,260,726	4,093,880	3,886,308
Liabilities:
Time deposits	$ 1,390,381	$ 1,489,072	$ 1,469,738