Commercial Mortgage Loans - Commercial Mortgage Loan Portfolio, Held-For-Investment (Details) - Commercial Mortgage Receivable, Held-For-Investment - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at Beginning of Year	$ 2,693,848	$ 2,762,042
Acquisitions and originations	921,104	1,287,720
Principal repayments	(470,936)	(1,223,490)
Discount accretion/premium amortization	2,852	6,146
Loans transferred from/(to) commercial real estate loans, held for sale	0	(76,979)
Net fees capitalized into carrying value of loans	(3,928)	(6,562)
(Provision)/benefit for credit losses	3,405	(13,181)
Charge-off from allowance	289	427
Transfer to real estate owned	(37,523)	(35,064)
Balance at End of Period	$ 3,109,111	2,693,848
Cumulative-effect adjustment upon adoption of ASU 2016-13 (Note 2)
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at Beginning of Year		$ (7,211)