Commitments and Contingencies - Lending Commitments (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Future funding commitments	$ 205.0	$ 276.6
Unfunded lending commitments for loans held for sale	1.4
Total unfunded commitments for equity method investments	39.3
Senior loans
Debt Instrument [Line Items]
Future funding commitments	164.2
Securitized loans
Debt Instrument [Line Items]
Future funding commitments	12.4
Corporate term loans
Debt Instrument [Line Items]
Future funding commitments	0.1
Mezzanine loans
Debt Instrument [Line Items]
Future funding commitments	$ 28.4