Commitments and Contingencies - Lending Commitments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Future funding commitments	$ 173.2	$ 276.6
Total unfunded commitments for equity method investments	24.6
Senior loans
Debt Instrument [Line Items]
Future funding commitments	146.3
Securitized loans
Debt Instrument [Line Items]
Future funding commitments	12.1
Corporate term loans
Debt Instrument [Line Items]
Future funding commitments	0.1
Mezzanine loans
Debt Instrument [Line Items]
Future funding commitments	$ 14.7