Commercial Mortgage Loans - Commercial Mortgage Loan Portfolio, Held-For-Investment (Details) - Commercial Mortgage Receivable, Held-For-Investment - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at Beginning of Year	$ 4,211,061	$ 2,693,848
Acquisitions and originations	640,033	2,897,002
Principal repayments	(320,511)	(1,286,598)
Discount accretion/premium amortization	2,542	7,038
Loans transferred from/(to) commercial real estate loans, held for sale	0	(52,615)
Net fees capitalized into carrying value of loans	(3,568)	(15,150)
(Provision)/benefit for credit losses	894	4,770
Charge-off from allowance	0	289
Transfer to real estate owned	0	(37,523)
Balance at End of Period	$ 4,530,451	$ 4,211,061