Loans and Allowance for Loan Losses - Loans by risk category (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Loans outstanding by loan portfolio segment and risk category
Loans	$ 1,686,087	$ 1,701,850
Pass
Loans outstanding by loan portfolio segment and risk category
Loans	1,625,938	1,614,365
Special Mention
Loans outstanding by loan portfolio segment and risk category
Loans	11,396	18,359
Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	48,497	67,563
Doubtful
Loans outstanding by loan portfolio segment and risk category
Loans	256	1,563
Commercial
Loans outstanding by loan portfolio segment and risk category
Loans	951,457	969,634
Commercial | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	894,163	884,653
Commercial | Special Mention
Loans outstanding by loan portfolio segment and risk category
Loans	11,396	18,359
Commercial | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	45,642	65,059
Commercial | Doubtful
Loans outstanding by loan portfolio segment and risk category
Loans	256	1,563
Commercial | Commercial and industrial
Loans outstanding by loan portfolio segment and risk category
Loans	485,183	510,706
Commercial | Commercial and industrial | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	453,707	459,565
Commercial | Commercial and industrial | Special Mention
Loans outstanding by loan portfolio segment and risk category
Loans	10,439	12,055
Commercial | Commercial and industrial | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	20,781	37,523
Commercial | Commercial and industrial | Doubtful
Loans outstanding by loan portfolio segment and risk category
Loans	256	1,563
Commercial | Real estate construction
Loans outstanding by loan portfolio segment and risk category
Loans	21,674	18,965
Commercial | Real estate construction | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	20,396	17,910
Commercial | Real estate construction | Special Mention
Loans outstanding by loan portfolio segment and risk category
Loans	284
Commercial | Real estate construction | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	994	1,055
Commercial | Commercial real estate
Loans outstanding by loan portfolio segment and risk category
Loans	444,600	439,963
Commercial | Commercial real estate | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	420,060	407,178
Commercial | Commercial real estate | Special Mention
Loans outstanding by loan portfolio segment and risk category
Loans	673	6,304
Commercial | Commercial real estate | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	23,867	26,481
Consumer
Loans outstanding by loan portfolio segment and risk category
Loans	734,630	732,216
Consumer | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	731,775	729,712
Consumer | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	2,855	2,504
Consumer | Residential | Real estate first mortgage
Loans outstanding by loan portfolio segment and risk category
Loans	459,763	448,143
Consumer | Residential | Real estate first mortgage | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	459,086	448,124
Consumer | Residential | Real estate first mortgage | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	677	19
Consumer | Residential | Real estate junior lien
Loans outstanding by loan portfolio segment and risk category
Loans	182,516	188,855
Consumer | Residential | Real estate junior lien | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	180,344	186,370
Consumer | Residential | Real estate junior lien | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	2,172	2,485
Consumer | Other revolving and installment
Loans outstanding by loan portfolio segment and risk category
Loans	92,351	95,218
Consumer | Other revolving and installment | Pass
Loans outstanding by loan portfolio segment and risk category
Loans	92,345	$ 95,218
Consumer | Other revolving and installment | Substandard
Loans outstanding by loan portfolio segment and risk category
Loans	$ 6