Other Assets - Investment in a Platform Partner (Details) - USD ($)		3 Months Ended	9 Months Ended		12 Months Ended
	Jul. 31, 2020	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2013	Dec. 31, 2019
Financing Receivable, Nonaccrual [Line Items]
Proceeds from sale of investment			$ 25,687,000	$ 0
Platform Partner | Series A Convertible Preferred Membership Units | Variable Interest Entity, Not Primary Beneficiary
Financing Receivable, Nonaccrual [Line Items]
Cash purchase of shares					$ 3,500,000
Shares purchased (in shares)					3,548,820
Platform Partner | Common Stock | Variable Interest Entity, Not Primary Beneficiary
Financing Receivable, Nonaccrual [Line Items]
Shares issued upon conversion (in shares)					3,548,820
Proceeds from sale of investment	$ 25,700,000
Gain on sale		$ 24,700,000	24,700,000
Platform Partner | Common Stock | Variable Interest Entity, Not Primary Beneficiary | Other Assets
Financing Receivable, Nonaccrual [Line Items]
Investment		$ 0	$ 0			$ 1,000,000.0