Fair Value Measurements (Schedule of Carrying Amounts and Estimated Fair Value of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Investment securities:
Available-for-sale	$ 680,644	$ 748,864	$ 657,818
Held-to-maturity	380,176	315,740	272,407
Carrying Amount [Member]
Investment securities:
Nonmarketable equity securities	31,249	27,369	25,572
Carrying Amount [Member] | Level 1[Member]
Assets:
Cash and cash equivalents	393,938	183,020	382,385
Investment securities:
Available-for-sale	8,302	8,259	0
Carrying Amount [Member] | Level 2 [Member]
Investment securities:
Available-for-sale	672,342	740,605	657,818
Held-to-maturity	370,950	305,913	267,599
Loans Held-for-sale	9,675	9,128	3,814
Interest receivable	19,816	17,492	16,945
Liabilities:
Deposits without defined maturities	4,988,268	4,741,024	3,868,700
Interest payable	779	755	876
Short-term borrowings	372,236	389,467	361,231
Carrying Amount [Member] | Level 3 [Member]
Investment securities:
Held-to-maturity	10,500	10,500	10,500
Net loans	5,627,618	5,612,547	4,674,816
Liabilities:
Time deposits	1,332,085	1,337,947	1,362,593
Fair Value [Member]
Investment securities:
Nonmarketable equity securities	31,249	27,369	25,572
Fair Value [Member] | Level 1[Member]
Assets:
Cash and cash equivalents	393,938	183,020	382,385
Investment securities:
Available-for-sale	8,302	8,259	0
Fair Value [Member] | Level 2 [Member]
Investment securities:
Available-for-sale	672,342	740,605	657,818
Held-to-maturity	372,876	308,650	265,947
Loans Held-for-sale	9,675	9,128	3,814
Interest receivable	19,816	17,492	16,945
Liabilities:
Deposits without defined maturities	4,988,268	4,741,024	3,868,700
Interest payable	779	755	876
Short-term borrowings	372,236	389,467	361,231
Fair Value [Member] | Level 3 [Member]
Investment securities:
Held-to-maturity	7,300	7,090	6,460
Net loans	5,633,217	5,623,454	4,688,814
Liabilities:
Time deposits	$ 1,335,605	$ 1,340,015	$ 1,371,312