Consolidated Statements of Income and Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest and dividend income
Interest and fees on loans (includes tax-exempt income of $1,302,000 in 2019, $1,157,000 in 2018, and $798,000 in 2017)	$ 59,239	$ 53,548	$ 45,373
Interest on deposits with other banks	188	242	52
Interest and dividends on investments (includes tax-exempt income of $7,333,000 in 2019, $6,954,000 in 2018, and $6,501,000 in 2017)	19,224	16,753	15,407
Total interest and dividend income	78,651	70,543	60,832
Interest expense
Interest on deposits	23,268	15,970	9,479
Interest on borrowed funds	2,890	4,364	4,050
Total interest expense	26,158	20,334	13,529
Net interest income	52,493	50,209	47,303
Provision for loan losses	1,250	1,500	2,000
Net interest income after provision for loan losses	51,243	48,709	45,303
Non-interest income
Net securities gains	224	137	471
Other operating income	6,408	5,674	5,463
Total non-interest income	14,189	12,600	12,548
Non-interest expense
Salaries and employee benefits	18,396	17,641	16,601
Occupancy expense	2,558	2,435	2,400
Furniture and equipment expense	3,990	3,924	3,681
FDIC insurance premiums	439	1,226	1,008
Amortization of identified intangibles	43	43	43
Other operating expense	9,746	8,198	7,918
Total non-interest expense	35,172	33,467	31,651
Income before income taxes	30,260	27,842	26,200
Applicable tax expense	4,735	4,306	6,612
Net income	$ 25,525	$ 23,536	$ 19,588
Basic earnings per common share (in usd per share)	$ 2.36	$ 2.18	$ 1.82
Diluted earnings per common share (in usd per share)	$ 2.34	$ 2.17	$ 1.81
Other comprehensive income (loss), net of tax
Net unrealized gain (loss) on securities available for sale	$ 8,708	$ (2,150)	$ (1,452)
Net unrealized gain (loss) on securities transferred from available for sale to held to maturity, net of amortization	15	(23)	(14)
Net unrealized gain (loss) on cash flow hedging derivative instruments	(1,341)	(106)	107
Net unrecognized gain (loss) on postretirement benefits	(13)	184	(19)
Other comprehensive gain (loss)	7,369	(2,095)	(1,378)
Comprehensive income	32,894	21,441	18,210
Fiduciary and investment management income
Non-interest income
Non-interest income	3,318	3,030	2,680
Service charges on deposit accounts
Non-interest income
Non-interest income	2,330	2,194	2,081
Mortgage origination and servicing income
Non-interest income
Non-interest income	$ 1,909	$ 1,565	$ 1,853