Loans and Allowance for Loan Losses - Loans by risk category (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Loans outstanding by loan portfolio segment and risk category
Loans	$ 1,758,277	$ 1,721,279
Pass
Loans outstanding by loan portfolio segment and risk category
Loans	1,690,909	1,654,719
Special Mention
Loans outstanding by loan portfolio segment and risk category
Loans	18,265	12,226
Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	49,086	54,334
Doubtful
Loans outstanding by loan portfolio segment and risk category
Loans	17
Commercial
Loans outstanding by loan portfolio segment and risk category
Loans	1,050,230	1,000,225
Commercial | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	988,242	935,719
Commercial | Special Mention
Loans outstanding by loan portfolio segment and risk category
Loans	14,879	12,226
Commercial | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	47,092	52,280
Commercial | Doubtful
Loans outstanding by loan portfolio segment and risk category
Loans	17
Commercial | Commercial and industrial
Loans outstanding by loan portfolio segment and risk category
Loans	502,637	479,144
Commercial | Commercial and industrial | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	470,867	448,306
Commercial | Commercial and industrial | Special Mention
Loans outstanding by loan portfolio segment and risk category
Loans	10,178	9,585
Commercial | Commercial and industrial | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	21,575	21,253
Commercial | Commercial and industrial | Doubtful
Loans outstanding by loan portfolio segment and risk category
Loans	17
Commercial | Real estate construction
Loans outstanding by loan portfolio segment and risk category
Loans	25,487	26,378
Commercial | Real estate construction | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	24,941	25,119
Commercial | Real estate construction | Special Mention
Loans outstanding by loan portfolio segment and risk category
Loans	279	282
Commercial | Real estate construction | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	267	977
Commercial | Commercial real estate
Loans outstanding by loan portfolio segment and risk category
Loans	522,106	494,703
Commercial | Commercial real estate | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	492,434	462,294
Commercial | Commercial real estate | Special Mention
Loans outstanding by loan portfolio segment and risk category
Loans	4,422	2,359
Commercial | Commercial real estate | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	25,250	30,050
Consumer
Loans outstanding by loan portfolio segment and risk category
Loans	708,047	721,054
Consumer | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	702,667	719,000
Consumer | Special Mention
Loans outstanding by loan portfolio segment and risk category
Loans	3,386
Consumer | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	1,994	2,054
Consumer | Residential | Real estate first mortgage
Loans outstanding by loan portfolio segment and risk category
Loans	457,895	457,155
Consumer | Residential | Real estate first mortgage | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	455,720	456,358
Consumer | Residential | Real estate first mortgage | Special Mention
Loans outstanding by loan portfolio segment and risk category
Loans	1,434
Consumer | Residential | Real estate first mortgage | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	741	797
Consumer | Residential | Real estate junior lien
Loans outstanding by loan portfolio segment and risk category
Loans	170,538	177,373
Consumer | Residential | Real estate junior lien | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	167,356	176,122
Consumer | Residential | Real estate junior lien | Special Mention
Loans outstanding by loan portfolio segment and risk category
Loans	1,952
Consumer | Residential | Real estate junior lien | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	1,230	1,251
Consumer | Other revolving and installment
Loans outstanding by loan portfolio segment and risk category
Loans	79,614	86,526
Consumer | Other revolving and installment | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	79,591	86,520
Consumer | Other revolving and installment | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	$ 23	$ 6