Fair Value of Financial Instruments, Part 3 (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Financial assets [Abstract]
Cash and cash equivalents	$ 678,585	$ 671,448	$ 621,548	$ 583,044
Securities available for sale	689,663	676,759
Held-to-maturity securities, carrying value	63,543	70,946
Held to maturity securities	67,689	75,342
Net loans, carrying value	3,197,377	3,112,005
Net loans	3,252,841	3,171,005
Accrued interest receivable	10,807	10,800
Financial liabilities [Abstract]
Demand deposits	355,783	331,425
Interest bearing deposits	3,781,923	3,700,828
Short-term borrowings	170,750	189,116
Accrued interest payable	515	548
Level 1 [Member]
Financial assets [Abstract]
Cash and cash equivalents	678,585	671,448
Securities available for sale	35	35
Held to maturity securities	0	0
Net loans	0	0
Accrued interest receivable	26	30
Financial liabilities [Abstract]
Demand deposits	355,783	331,425
Interest bearing deposits	2,596,394	2,537,583
Short-term borrowings	0	0
Accrued interest payable	77	100
Level 2 [Member]
Financial assets [Abstract]
Cash and cash equivalents	0	0
Securities available for sale	689,628	676,724
Held to maturity securities	67,689	75,342
Net loans	0	0
Accrued interest receivable	2,652	2,694
Financial liabilities [Abstract]
Demand deposits	0	0
Interest bearing deposits	1,185,529	1,163,245
Short-term borrowings	170,750	189,116
Accrued interest payable	438	448
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	3,252,841	3,171,005
Accrued interest receivable	8,129	8,076
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	678,585	671,448
Securities available for sale	689,663	676,759
Held-to-maturity securities, carrying value	63,543	70,946
Federal Reserve Bank and Federal Home Loan Bank stock	9,480	9,228
Net loans, carrying value	3,197,377	3,112,005
Accrued interest receivable	10,807	10,800
Financial liabilities [Abstract]
Demand deposits	355,783	331,425
Interest bearing deposits, carrying value	3,781,658	3,700,816
Short-term borrowings	170,750	189,116
Accrued interest payable	$ 515	$ 548