Fair Value Measurements (Schedule of Carrying Amounts and Estimated Fair Value of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Investment securities:
Available-for-sale	$ 657,818	$ 684,570	$ 703,622
Held-to-maturity	272,407	268,271	261,405
Carrying Amount [Member]
Investment securities:
Available-for-sale	0	0	4,755
Nonmarketable equity securities	25,572	25,572	25,572
Carrying Amount [Member] | Level 1[Member]
Assets:
Cash and cash equivalents	382,385	310,788	578,726
Carrying Amount [Member] | Level 2 [Member]
Investment securities:
Available-for-sale	657,818	684,570	698,867
Held-to-maturity	267,599	263,405	257,749
Loans Held-for-sale	3,814	5,219	14,850
Interest receivable	16,945	15,748	16,960
Liabilities:
Deposits without defined maturities	3,868,700	3,790,454	3,574,832
Interest payable	876	868	1,338
Short-term borrowings	361,231	327,428	347,484
Carrying Amount [Member] | Level 3 [Member]
Investment securities:
Held-to-maturity	10,500	10,500	0
Net loans	4,674,816	4,568,549	4,102,427
Liabilities:
Time deposits	1,362,593	1,331,931	1,432,526
Fair Value [Member]
Investment securities:
Available-for-sale	0	0	4,755
Nonmarketable equity securities	25,572	25,572	25,572
Fair Value [Member] | Level 1[Member]
Assets:
Cash and cash equivalents	382,385	310,788	578,726
Fair Value [Member] | Level 2 [Member]
Investment securities:
Available-for-sale	657,818	684,570	698,867
Held-to-maturity	265,947	262,021	261,405
Loans Held-for-sale	3,814	5,219	14,850
Interest receivable	16,945	15,748	16,960
Liabilities:
Deposits without defined maturities	3,868,700	3,790,454	3,574,832
Interest payable	876	868	1,338
Short-term borrowings	361,231	327,428	347,484
Fair Value [Member] | Level 3 [Member]
Investment securities:
Held-to-maturity	6,460	6,250	0
Net loans	4,688,814	4,575,532	4,123,585
Liabilities:
Time deposits	$ 1,371,312	$ 1,340,746	$ 1,448,634