Commitments and Contingencies - Allowance for Credit Losses for Unfunded Loan Commitments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2020
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Balance at beginning of period	$ 7,004	$ 2,346	$ 3,112	$ 2,139	$ 2,139
Impact of adopting ASU 2016-13 at January 1, 2020	5,188	2,441	5,188	2,139	2,139	$ 2,139	$ 3,113
Provision for credit losses	(1,816)	95	727	302
Balance at end of period	$ 5,188	$ 2,441	$ 5,188	2,441	$ 3,112	$ 2,139
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201602Member
Impact of ASU 2016-13 Adoption
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Balance at beginning of period			$ 1,349	0	$ 0
Impact of adopting ASU 2016-13 at January 1, 2020			1,349	0	0	$ 0	1,349
Balance at end of period					1,349	0
Adjusted Balance
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Balance at beginning of period			4,461	2,139	2,139
Impact of adopting ASU 2016-13 at January 1, 2020			$ 4,461	$ 2,139	2,139	2,139	$ 4,462
Balance at end of period					$ 4,461	$ 2,139