Fair Value Measurements - Summary of Changes in Assets and Liabilities With Level III Fair Values (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2021 USD ($)
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance as of December 31, 2020	$ 7,889,801
Change in fair value	609,169
Balance as of June 30, 2021	8,498,970
Loans Held for Investment
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance as of December 31, 2020	4,472,984
Change in fair value	306,500
Balance as of June 30, 2021	4,779,484
Collateralized Loan Obligation
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance as of December 31, 2020	1,834,760
Change in fair value	984,880
Balance as of June 30, 2021	2,819,640
Secured Financing Agreements
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance as of December 31, 2020	1,532,910
Change in fair value	(682,352)
Balance as of June 30, 2021	850,558
Mortgage Loan Payable
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance as of December 31, 2020	49,147
Change in fair value	141
Balance as of June 30, 2021	$ 49,288