Fair Value of Financial Instruments, Part 3 (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013	Dec. 31, 2012
Financial assets [Abstract]
Cash and cash equivalents	$ 621,548	$ 583,044	$ 628,832	$ 544,016
Securities available for sale	811,770	863,754
Held-to-maturity securities	77,926	86,215
Held to maturity securities	82,895	90,305
Net loans	2,959,215	2,861,095
Net loans	3,002,229	2,910,940
Accrued interest receivable	11,350	11,198
Financial liabilities [Abstract]
Demand deposits	324,277	318,456
Interest bearing deposits	3,671,524	3,609,592
Short-term borrowings	181,516	204,162
Accrued interest payable	466	468
Level 1 [Member]
Financial assets [Abstract]
Cash and cash equivalents	621,548	583,044
Securities available for sale	35	10
Held to maturity securities	0	0
Net loans	0	0
Accrued interest receivable	0	0
Financial liabilities [Abstract]
Demand deposits	324,277	318,456
Interest bearing deposits	2,528,187	2,477,567
Short-term borrowings	0	0
Accrued interest payable	100	101
Level 2 [Member]
Financial assets [Abstract]
Cash and cash equivalents	0	0
Securities available for sale	811,735	863,744
Held to maturity securities	82,895	90,305
Net loans	0	0
Accrued interest receivable	3,233	3,452
Financial liabilities [Abstract]
Demand deposits	0	0
Interest bearing deposits	1,143,337	1,132,025
Short-term borrowings	181,516	204,162
Accrued interest payable	366	367
Level 3 [Member]
Financial assets [Abstract]
Cash and cash equivalents	0	0
Securities available for sale	0	0
Held to maturity securities	0	0
Net loans	3,002,229	2,910,940
Accrued interest receivable	8,117	7,746
Financial liabilities [Abstract]
Demand deposits	0	0
Interest bearing deposits	0	0
Short-term borrowings	0	0
Accrued interest payable	0	0
Carrying Value [Member]
Financial assets [Abstract]
Cash and cash equivalents	621,548	583,044
Securities available for sale	811,770	863,754
Held-to-maturity securities	77,926	86,215
Federal Reserve Bank and Federal Home Loan Bank stock	10,951	10,500
Net loans	2,959,215	2,861,095
Accrued interest receivable	11,350	11,198
Financial liabilities [Abstract]
Demand deposits	324,277	318,456
Interest bearing deposits	3,670,910	3,608,615
Short-term borrowings	181,516	204,162
Accrued interest payable	$ 466	$ 468