Loans (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Apr. 01, 2019	Jul. 01, 2018
Financing Receivable, Impaired [Line Items]
PPP loans originated	$ 543,100,000	$ 337,100,000
SBA PPP Fees received		20,200,000
PPP loans		337,100,000
SBA PPP Fees recognized		13,700,000
Loans and Leases Receivable, Deferred Income		23,600,000	$ 16,300,000
Goodwill, Purchase Accounting Adjustments		(2,403,000)	(3,373,000)	$ (793,000)
Deposit Liabilities Reclassified as Loans Receivable		2,000,000.0	2,200,000
Business Combination, Acquired Receivables, Gross Contractual Amount					$ 589,698,000	$ 277,900,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables					578,577,000	272,800,000
Business Combination, Acquired Receivable, Fair Value					578,577,000
Specific Reserves Related To Troubled Debt Restructuring		200,000	2,200,000
TDRs included in nonaccrual loan totals		25,800,000	34,300,000
Consumer Loan [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivables, COVID Modifications, Recorded Investment, During Period		103,500,000
Consumer Loan [Member] | Other Restructuring
Financing Receivable, Impaired [Line Items]
Financing Receivables, COVID Modifications, Recorded Investment, During Period		2,100,000
Consumer Loan [Member] | Covid Restructuring
Financing Receivable, Impaired [Line Items]
Financing Receivables, COVID Modifications, Recorded Investment, During Period		949,000
Commercial Portfolio Segment [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivables, COVID Modifications, Recorded Investment, During Period		563,700,000
Commercial Portfolio Segment [Member] | Other Restructuring
Financing Receivable, Impaired [Line Items]
Financing Receivables, COVID Modifications, Recorded Investment, During Period		6,300,000
Commercial Portfolio Segment [Member] | Covid Restructuring
Financing Receivable, Impaired [Line Items]
Financing Receivables, COVID Modifications, Recorded Investment, During Period		109,000
Executive officers and directors
Financing Receivable, Impaired [Line Items]
Loans due from related party		51,300,000	44,300,000
Loans and Leases Receivable, Related Parties, Additions		600,000	9,200,000
Loans and Leases Receivable, Related Parties, Proceeds		9,700,000	15,300,000
LoansAndLeasesReceivableRelatedPartiesAdvances		12,400,000	8,900,000
Executive officers and directors | Loans
Financing Receivable, Impaired [Line Items]
Loans due from related party		32,000,000.0	28,700,000
Carolina Alliance [Member]
Financing Receivable, Impaired [Line Items]
Business Combination, Acquired Receivables, Estimated Uncollectible		9,500,000	11,300,000
Financial Asset Acquired with Credit Deterioration [Member]
Financing Receivable, Impaired [Line Items]
Business Combination, Acquired Receivables, Gross Contractual Amount		1,700,000	3,200,000			5,100,000
Business Combination, Acquired Receivable, Fair Value		1,600,000	3,000,000.0			$ 4,900,000
Financial Asset Acquired with Credit Deterioration [Member] | NewDominion [Member]
Financing Receivable, Impaired [Line Items]
Allowance for Loan and Lease Losses, Loans Acquired		1,000	101,000
Financial Asset Acquired with Credit Deterioration [Member] | Carolina Alliance [Member]
Financing Receivable, Impaired [Line Items]
Business Combination, Acquired Receivables, Gross Contractual Amount		11,800,000	13,800,000		19,900,000
Business Combination, Acquired Receivable, Fair Value					$ 18,400,000
Allowance for Loan and Lease Losses, Loans Acquired		166,000	167,000
Loans
Financing Receivable, Impaired [Line Items]
Goodwill, Purchase Accounting Adjustments		7,200,000	$ 11,700,000
PPP Loans
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Deferred Income		$ 6,500,000