Loans and Allowance for Credit Losses - Narrative (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($) commitment	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) commitment contract	Sep. 30, 2020 USD ($) contract	Dec. 31, 2020 USD ($) contract	Jun. 30, 2021 USD ($)	Jan. 01, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net deferred origination fees	$ 14,900,000		$ 14,900,000		$ 11,735,000
Premiums (discounts) associated with acquired loans	(9,000)		(9,000)		(47,000)
Accrued interest on loans	6,300,000		6,300,000		7,100,000
PPP loans	1,436,841,000		1,436,841,000		1,422,914,000
ACL	13,816,000	$ 21,683,000	13,816,000	$ 21,683,000	21,136,000	$ 14,539,000		$ 20,653,000	$ 19,088,000
Nonaccrual loans	12,493,000		12,493,000		11,120,000
Interest on nonaccrual loans reversed through interest income	0	0	0	12,000
Interest earned on nonaccrual loans	198,000	780,000	565,000	$ 986,000
Total loans classified as TDRs	$ 7,036,000		$ 7,036,000		$ 7,900,000
Number of commitments on TDR | commitment	0		0
Charge offs on loans later classified as TDRs			$ 0
TDR with specific impairment | contract					0
Number of TDRs that defaulted within twelve months of restructure | contract			0	0
Cumulative effect, period of adoption, adjusted balance
Accounts, Notes, Loans and Financing Receivable [Line Items]
ACL							$ 16,600,000
Net of government guarantees
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 11,476,000		$ 11,476,000		$ 9,637,000
Commercial & industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
ACL	3,982,000	$ 8,195,000	3,982,000	$ 8,195,000	7,973,000	$ 4,291,000		$ 7,366,000	$ 6,604,000
Nonaccrual loans	4,974,000		4,974,000		3,848,000
Commercial & industrial loans | Small Business Administration (SBA), CARES Act, Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
PPP loans	$ 203,400,000		$ 203,400,000		$ 304,600,000