Allowance for Credit Losses - Unfunded Loan Commitments (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Allowance for loan losses:
Beginning balance	$ 17,335	$ 946
Accounting standards update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member
Provision for credit losses on unfunded loan commitments (included in other noninterest expense)	2,700	$ 8,700
Ending balance	$ 20,035	20,035	$ 946
Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses:
Beginning balance		$ 10,389
Ending balance			$ 10,389