Loans and Credit Quality - Narrative (Details)		9 Months Ended	12 Months Ended
	Apr. 01, 2014 USD ($) purchased_loan	Sep. 30, 2017 USD ($) contract financing_commitment	Dec. 31, 2016 USD ($) contract
Receivables [Abstract]
Net nonaccrual loans		$ 22,494,000	$ 12,480,000
Nonperforming loans minimum threshold for individual impairment evaluation		50,000
Recorded investment in loans considered to be impaired		39,722,000	38,656,000
Business Acquisition [Line Items]
Total		$ 25,968,000	$ 16,200,000
Number of commitments on TDR | financing_commitment		0
Charge offs on loans later classified as TDRs		$ 731,000
TDR with specific impairment | contract		4	4
TDR that subsequently defaulted | contract		0	0
Alaska Pacific Bancshares
Business Acquisition [Line Items]
Purchased impaired loans | purchased_loan	18
Accretable yield on purchased loans	$ 0
Fair value of purchased credit impaired loans	$ 3,900,000	$ 942,000