Fair Value Measurements (Schedule of Carrying Amounts and Estimated Fair Value of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Investment securities:
Available-for-sale	$ 576,211	$ 684,570	$ 705,146
Held-to-maturity	314,275	268,271	275,866
Carrying Amount [Member]
Investment securities:
Nonmarketable equity securities	25,572	25,572	25,572
Carrying Amount [Member] | Level 1[Member]
Assets:
Cash and cash equivalents	382,138	310,788	493,110
Carrying Amount [Member] | Level 2 [Member]
Investment securities:
Available-for-sale	576,211	684,570	705,146
Held-to-maturity	308,062	263,405	272,079
Loans Held-for-sale	9,347	5,219	7,907
Interest receivable	17,057	15,748	16,359
Liabilities:
Deposits without defined maturities	4,191,894	3,790,454	3,842,148
Interest payable	710	868	1,009
Short-term borrowings	323,086	327,428	357,595
Carrying Amount [Member] | Level 3 [Member]
Investment securities:
Held-to-maturity	10,500	10,500	10,500
Net loans	4,963,914	4,568,549	4,441,139
Liabilities:
Time deposits	1,240,033	1,331,931	1,349,157
Fair Value [Member]
Investment securities:
Nonmarketable equity securities	25,572	25,572	25,572
Fair Value [Member] | Level 1[Member]
Assets:
Cash and cash equivalents	382,138	310,788	493,110
Fair Value [Member] | Level 2 [Member]
Investment securities:
Available-for-sale	576,211	684,570	705,146
Held-to-maturity	307,290	262,021	269,616
Loans Held-for-sale	9,347	5,219	7,907
Interest receivable	17,057	15,748	16,359
Liabilities:
Deposits without defined maturities	4,191,894	3,790,454	3,842,148
Interest payable	710	868	1,009
Short-term borrowings	323,086	327,428	357,595
Fair Value [Member] | Level 3 [Member]
Investment securities:
Held-to-maturity	6,985	6,250	6,250
Net loans	4,967,167	4,575,532	4,446,796
Liabilities:
Time deposits	$ 1,242,419	$ 1,340,746	$ 1,359,739