Commitments and Contingencies - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitment to contribute capital	$ 78,600		$ 55,500
Reserve for Unfunded Loan Commitments	$ 76,071	$ 74,571	$ 85,571	$ 96,571	$ 80,571	$ 39,571	$ 35,861