Fair Value of Financial Instruments, Part 3 (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Financial assets [Abstract]
Cash and cash equivalents	$ 630,655	$ 583,044	$ 555,649	$ 544,016
Securities available for sale	722,623	863,754
Held-to-maturity securities, carrying value	74,179	86,215
Held to maturity securities	78,693	90,305
Net loans, carrying value	3,036,517	2,861,095
Net loans	3,085,228	2,910,940
Accrued interest receivable	10,791	11,198
Financial liabilities [Abstract]
Demand deposits	327,527	318,456
Interest bearing deposits	3,658,068	3,609,592
Short-term borrowings	179,957	204,162
Accrued interest payable	500	468
Level 1 [Member]
Financial assets [Abstract]
Cash and cash equivalents	630,655	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	327,527	318,456
Interest bearing deposits	2,517,595	2,477,567
Short-term borrowings	0	0
Accrued interest payable	98	101
Level 2 [Member]
Financial assets [Abstract]
Cash and cash equivalents	0	0
Securities available for sale	722,588	863,744
Held to maturity securities	78,693	90,305
Net loans	0	0
Accrued interest receivable	2,766	3,452
Financial liabilities [Abstract]
Demand deposits	0	0
Interest bearing deposits	1,140,473	1,132,025
Short-term borrowings	179,957	204,162
Accrued interest payable	402	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	3,085,228	2,910,940
Accrued interest receivable	8,025	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	630,655	583,044
Securities available for sale	722,623	863,754
Held-to-maturity securities, carrying value	74,179	86,215
Federal Reserve Bank and Federal Home Loan Bank stock	9,228	10,500
Net loans, carrying value	3,036,517	2,861,095
Accrued interest receivable	10,791	11,198
Financial liabilities [Abstract]
Demand deposits	327,527	318,456
Interest bearing deposits	3,657,514	3,608,615
Short-term borrowings	179,957	204,162
Accrued interest payable	$ 500	$ 468