Variable Interest Entities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) item	Mar. 31, 2021 USD ($) item
Variable interest entities
Total Assets	$ 80,873,509	$ 79,702,323
Total Liabilities	76,010,933	$ 74,847,538
Number of collateralized debt obligation | item		0
Investment in unconsolidated entities	108,054	$ 100,907
CMBS JV
Variable interest entities
Ownership percentage		51.00%
Primary beneficiary
Variable interest entities
Total Assets	64,238,328	$ 62,367,110
Total Liabilities	$ 62,776,371	60,896,709
Primary beneficiary | ASU 2015-02
Variable interest entities
Total Assets		98,700
Total Liabilities		53,800
Primary beneficiary | CMBS Venture Holdings
Variable interest entities
Total Assets		335,400
Total Liabilities		78,900
Primary beneficiary | SPT Dolphin | ASU 2015-02
Variable interest entities
Total Assets		685,400
Total Liabilities		$ 520,600
Not primary beneficiary
Variable interest entities
Number of CDO structures currently in default | item		5
Number of CDO structures | item	5	6
Number of CDO structures that entered default during the period | item	2
Maximum risk of loss related to VIEs, on fair value basis		$ 19,300
Not primary beneficiary | ASU 2015-02 | Measurement Period Adjustments
Variable interest entities
Investment in unconsolidated entities		25,700
Not primary beneficiary | Securitization SPEs
Variable interest entities
Debt obligations to beneficial interest holders, unpaid principal balances		$ 3,900,000