Loans and Credit Quality - Narrative (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) contract financing_commitment	Mar. 31, 2018 contract	Dec. 31, 2018 USD ($) contract
Receivables [Abstract]
Net nonaccrual loans	$ 18,478,000		$ 14,694,000
Nonperforming loans minimum threshold for individual impairment evaluation	50,000
Recorded investment in loans considered to be impaired	$ 31,085,000		31,714,000
Number of newly restructured loans | contract	0
Total loans classified as troubled debt restructurings	$ 13,167,000		$ 14,800,000
Number of commitments on TDR | financing_commitment	0
Charge offs on loans later classified as TDRs	$ 0
TDR with specific impairment | contract	1		1
TDR that subsequently defaulted | contract	5	0