Loans and Credit Quality - Narrative (Details)	9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) contract financing_commitment	Sep. 30, 2019 contract	Dec. 31, 2019 USD ($) contract
Accounts, Notes, Loans and Financing Receivable [Line Items]
PPP loans	$ 1,507,205,000		$ 1,048,456,000
Net nonaccrual loans	11,047,000		13,951,000
Total loans classified as troubled debt restructurings	$ 8,476,000		$ 10,100,000
Number of commitments on TDR | financing_commitment	0
Charge offs on loans later classified as TDRs	$ 0
TDR with specific impairment | contract	0		0
TDR that subsequently defaulted, number of contracts | contract	0	0
Small Business Administration (SBA), CARES Act, Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unearned origination fees, net of origination costs	$ 8,800,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
PPP loans	836,178,000		$ 412,690,000
Commercial | Small Business Administration (SBA), CARES Act, Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
PPP loans	$ 375,600,000