Segment Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($) office	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) segment office	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segment									3
Net Interest Income	$ 19,438	$ 18,859	$ 18,706	$ 18,549	$ 19,031	$ 18,791	$ 18,321	$ 18,196	$ 75,552	$ 74,339	$ 68,517
Net Gains on Sales of Loans									2,959	1,892	2,645
Net Gains on Securities									725	1,481	2,429
Trust and Investment Product Fees									3,957	3,675	3,358
Insurance Revenues									7,489	7,255	6,217
Noncash Items:
Provision for Loan Losses									0	150	350
Depreciation and Amortization									4,264	4,810	4,461
Income Tax Expense (Benefit)									11,606	12,069	11,464
Segment Profit (Loss)	7,712	$ 7,721	$ 7,325	$ 7,306	7,644	$ 7,708	$ 6,687	$ 6,305	30,064	28,344	25,413
Segment Assets	$ 2,373,701				2,237,099				$ 2,373,701	2,237,099	2,163,827
Core Banking
Segment Reporting Information [Line Items]
Number of offices | office	37								37
Net Interest Income									$ 75,939	74,801	69,634
Net Gains on Sales of Loans									2,959	1,892	2,645
Net Gains on Securities									698	1,481	2,065
Trust and Investment Product Fees									3	4	6
Insurance Revenues									24	29	39
Noncash Items:
Provision for Loan Losses									0	150	350
Depreciation and Amortization									3,994	4,527	3,944
Income Tax Expense (Benefit)									11,836	12,258	12,387
Segment Profit (Loss)									29,461	27,589	25,389
Segment Assets	$ 2,367,296				2,242,456				2,367,296	2,242,456	2,171,837
Trust and Investment Advisory Services
Segment Reporting Information [Line Items]
Net Interest Income									8	16	21
Net Gains on Sales of Loans									0	0	0
Net Gains on Securities									0	0	0
Trust and Investment Product Fees									3,957	3,671	3,355
Insurance Revenues									33	38	31
Noncash Items:
Provision for Loan Losses									0	0	0
Depreciation and Amortization									13	23	28
Income Tax Expense (Benefit)									(24)	(156)	(32)
Segment Profit (Loss)									(70)	(259)	(70)
Segment Assets	1,338				11,401				1,338	11,401	11,663
Insurance
Segment Reporting Information [Line Items]
Net Interest Income									6	4	17
Net Gains on Sales of Loans									0	0	0
Net Gains on Securities									0	0	0
Trust and Investment Product Fees									0	0	0
Insurance Revenues									7,432	7,188	6,147
Noncash Items:
Provision for Loan Losses									0	0	0
Depreciation and Amortization									107	110	339
Income Tax Expense (Benefit)									663	737	320
Segment Profit (Loss)									1,003	1,059	425
Segment Assets	7,022				6,429				7,022	6,429	5,636
Other
Segment Reporting Information [Line Items]
Net Interest Income									(401)	(482)	(1,155)
Net Gains on Sales of Loans									0	0	0
Net Gains on Securities									27	0	364
Trust and Investment Product Fees									(3)	0	(3)
Insurance Revenues									0	0	0
Noncash Items:
Provision for Loan Losses									0	0	0
Depreciation and Amortization									150	150	150
Income Tax Expense (Benefit)									(869)	(770)	(1,211)
Segment Profit (Loss)									(330)	(45)	(331)
Segment Assets	$ (1,955)				$ (23,187)				$ (1,955)	$ (23,187)	$ (25,309)