Segment Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($) office	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) segment office	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of primary segments | segment									3
Net Interest Income	$ 25,454	$ 24,917	$ 24,813	$ 24,725	$ 24,889	$ 24,560	$ 24,671	$ 20,784	$ 99,909	$ 94,904	$ 75,552
Net Gains on Sales of Loans									3,280	3,359	2,959
Net Gains on Securities									596	1,979	725
Trust and Investment Product Fees									5,272	4,644	3,957
Insurance Revenues									7,979	7,741	7,489
Noncash Items:
Provision for Loan Losses									1,750	1,200	0
Depreciation and Amortization									4,687	4,315	4,264
Income Tax Expense (Benefit)									11,534	13,946	11,606
Segment Profit (Loss)	11,621	$ 9,660	$ 9,839	$ 9,556	10,065	$ 10,185	$ 9,788	$ 5,146	40,676	35,184	30,064
Segment Assets	3,144,360				2,955,994				3,144,360	2,955,994	2,373,701
Other
Segment Reporting Information [Line Items]
Net Interest Income									(765)	(666)	(401)
Net Gains on Sales of Loans									0	0	0
Net Gains on Securities									3	0	27
Trust and Investment Product Fees									(3)	(15)	(3)
Insurance Revenues									0	0	0
Noncash Items:
Provision for Loan Losses									0	0	0
Depreciation and Amortization									256	238	150
Income Tax Expense (Benefit)									(1,385)	(1,269)	(869)
Segment Profit (Loss)									21	(1,260)	(330)
Segment Assets	$ (9,801)				(12,936)				$ (9,801)	(12,936)	(1,955)
Core Banking
Segment Reporting Information [Line Items]
Number of banking offices | office	53								53
Core Banking | Operating Segments
Segment Reporting Information [Line Items]
Net Interest Income									$ 100,659	95,562	75,939
Net Gains on Sales of Loans									3,280	3,359	2,959
Net Gains on Securities									593	1,979	698
Trust and Investment Product Fees									3	(3)	3
Insurance Revenues									28	23	24
Noncash Items:
Provision for Loan Losses									1,750	1,200	0
Depreciation and Amortization									4,351	4,002	3,994
Income Tax Expense (Benefit)									12,262	14,306	11,836
Segment Profit (Loss)									39,520	35,070	29,461
Segment Assets	$ 3,142,096				2,958,585				3,142,096	2,958,585	2,367,296
Trust and Investment Advisory Services | Operating Segments
Segment Reporting Information [Line Items]
Net Interest Income									6	1	8
Net Gains on Sales of Loans									0	0	0
Net Gains on Securities									0	0	0
Trust and Investment Product Fees									5,272	4,662	3,957
Insurance Revenues									34	29	33
Noncash Items:
Provision for Loan Losses									0	0	0
Depreciation and Amortization									4	3	13
Income Tax Expense (Benefit)									145	168	(24)
Segment Profit (Loss)									217	227	(70)
Segment Assets	1,987				1,851				1,987	1,851	1,338
Insurance | Operating Segments
Segment Reporting Information [Line Items]
Net Interest Income									9	7	6
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									7,917	7,689	7,432
Noncash Items:
Provision for Loan Losses									0	0	0
Depreciation and Amortization									76	72	107
Income Tax Expense (Benefit)									512	741	663
Segment Profit (Loss)									918	1,147	1,003
Segment Assets	$ 10,078				$ 8,494				$ 10,078	$ 8,494	$ 7,022