Loans and Investments - Loan Modifications (Details) $ in Thousands	1 Months Ended	3 Months Ended				6 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) loan	Mar. 31, 2024 USD ($) loan	Dec. 31, 2023 USD ($) loan	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) loan	Dec. 31, 2023 USD ($) loan
Financing Receivable, Modified [Line Items]
Loans and investments, gross		$ 11,873,208		$ 12,615,006		$ 11,873,208	$ 12,615,006
New borrower investments		$ 4,900	$ 2,000
Number of impaired loans (less unearned revenue and other holdbacks and adjustments) by asset class | loan		25		19		25	19
Interest reserve						$ 185,400	$ 156,100
Future funding commitments, modified loans, borrowers experiencing financial difficulty		$ 43,800				$ 43,800
Loan modification, refinancing, and extensions | loan		0				0	0
Secondary Loan
Financing Receivable, Modified [Line Items]
Financing receivable, net of reserve		$ 4,400				$ 4,400
Loans modified in period, floor interest rate spread		0.0375
Senior Lien
Financing Receivable, Modified [Line Items]
Financing receivable, basis spread on variable rate		0.0050				0.0050
Financing receivable, floor interest rate		0.0600
Loans modified in period, floor interest rate spread		0.0325
Senior Lien | Senior Position Loan
Financing Receivable, Modified [Line Items]
Financing receivable, net of reserve		$ 32,000				$ 32,000
Financial Asset, 60 Days Past Due
Financing Receivable, Modified [Line Items]
Loans and investments, gross		$ 36,400				$ 36,400
Financing receivable, specific reserve				$ 5,000
Financing receivable, net of reserve				$ 31,400			$ 31,400
Temporary Interest Rate Relief
Financing Receivable, Modified [Line Items]
Number of loans modified not pursuant to contract | loan		2	4	2		2	2
Loans modified, not pursuant to contract, amount		$ 66,800	$ 122,300				$ 55,500
Loan loss reserves related to VIEs				$ 14,000			14,000
Bridge loans
Financing Receivable, Modified [Line Items]
Variable rate, spread					3.40%
Financing receivable, accrual rate	0.0300
Loans and investments, gross		$ 11,478,252	13,500	12,273,244	$ 70,500	$ 11,478,252	12,273,244
Financing receivable, specific reserve			$ 1,500
Loans modified in period, floor interest rate spread			0.0415
Fixed interest rate, first twenty four months			0.0825
Fixed interest rate, last twelve months			0.0850
Financing receivable, fixed interest rate	0.0300
Financing receivable, total fixed rate	0.0600
Financing receivable, total fixed rate, period	18 months
Financing receivable, borrower required funding	$ 10,500
Interest reserve	2,500
Financing receivable, borrower requirement, capital improvements	$ 8,000
Financing receivable, borrower requirement, capital improvements, period	15 months
Bridge loans | Loan Reduction
Financing Receivable, Modified [Line Items]
Loans and investments, gross			$ 12,500
Multifamily | Bridge loans
Financing Receivable, Modified [Line Items]
Number of financing receivables modified during the period | loan			16
Financing receivable, amount modified in period			$ 692,800
Weighted average pay rate		0.0730	0.0695
Financing receivable, accrual rate		0.0204	0.0186
Loans previously classified as non-performing			$ 712,900
Multifamily | Bridge loans | Financial Asset, Less Than 60 Days Past Due
Financing Receivable, Modified [Line Items]
Loans previously classified as non-performing		$ 92,700				92,700
Multifamily | Bridge loans | Greater Than 60 Days Past Due
Financing Receivable, Modified [Line Items]
Loans previously classified as non-performing		$ 12,200				$ 12,200
Multifamily | Bridge loans | Minimum
Financing Receivable, Modified [Line Items]
Variable rate, spread		3.25%	3.25%
Multifamily | Bridge loans | Maximum
Financing Receivable, Modified [Line Items]
Variable rate, spread		5.25%	4.25%
Multifamily | Bridge loans | Temporary Interest Rate Relief And Extended Maturity
Financing Receivable, Modified [Line Items]
Number of financing receivables modified during the period | loan		14
Financing receivable, amount modified in period		$ 291,900	$ 671,000
Number of financing receivables with extended maturities | loan		12	15
Multifamily | Bridge loans | Temporary Interest Rate Relief And Extended Maturity | Minimum
Financing Receivable, Modified [Line Items]
Financing receivable modified, weighted average term increase from modification		4 months	12 months
Multifamily | Bridge loans | Temporary Interest Rate Relief And Extended Maturity | Maximum
Financing Receivable, Modified [Line Items]
Financing receivable modified, weighted average term increase from modification		23 months	30 months
Multifamily | Bridge loans | Temporary Interest Rate Relief And Extended Maturity, Fourteen Loans
Financing Receivable, Modified [Line Items]
Financing receivable, amount modified in period		$ 361,800
Multifamily | Bridge loans | Extended Maturity
Financing Receivable, Modified [Line Items]
Number of financing receivables modified during the period | loan		12
Financing receivable, amount modified in period		$ 201,900
Number of financing receivables with extended maturities | loan		8
Multifamily | Bridge loans | Extended Maturity | Minimum
Financing Receivable, Modified [Line Items]
Financing receivable modified, weighted average term increase from modification		6 months
Multifamily | Bridge loans | Extended Maturity | Maximum
Financing Receivable, Modified [Line Items]
Financing receivable modified, weighted average term increase from modification		15 months
Multifamily | Bridge loans | Loan Modification, Extended Maturity, Twelve Loans
Financing Receivable, Modified [Line Items]
Financing receivable, amount modified in period		$ 321,700
Multifamily | Bridge loans | Temporary Interest Rate Relief, Twenty Three Loans
Financing Receivable, Modified [Line Items]
Number of financing receivables modified during the period | loan			23
Financing receivable, amount modified in period			$ 1,070,000
Multifamily | Bridge loans | Temporary Interest Rate Relief
Financing Receivable, Modified [Line Items]
Number of impaired loans (less unearned revenue and other holdbacks and adjustments) by asset class | loan			2
Loan loss reserve, specifically impaired loans			$ 7,000
Total UPB, specifically impaired loans			$ 49,600
Multifamily | Bridge loans | Extended Maturity
Financing Receivable, Modified [Line Items]
Number of financing receivables modified during the period | loan			11
Financing receivable, amount modified in period			$ 456,500
Multifamily | Bridge loans | Extended Maturity | Minimum
Financing Receivable, Modified [Line Items]
Financing receivable modified, weighted average term increase from modification			2 months
Multifamily | Bridge loans | Extended Maturity | Maximum
Financing Receivable, Modified [Line Items]
Financing receivable modified, weighted average term increase from modification			19 months
Multifamily | Bridge loans | Rate of Interest and Extended Maturity
Financing Receivable, Modified [Line Items]
Financing receivable, amount modified in period				$ 86,900
Variable rate, spread				4.25%
Financing receivable modified, weighted average term increase from modification				1 year
Financing receivable modified, pay rate of interest				$ 500
Multifamily | Bridge loans | Interest Deferral, Extended Maturity, And Interest Forgiveness
Financing Receivable, Modified [Line Items]
Number of financing receivables modified during the period | loan				3
Financing receivable, amount modified in period				$ 241,000
Financing receivable modified, weighted average term increase from modification				1 year
Percentage of deferred interest waived				0.25
Multifamily | Bridge loans | Interest Deferral, Extended Maturity, And Interest Forgiveness | Minimum
Financing Receivable, Modified [Line Items]
Variable rate, spread				4.00%
Percentage of interest foregone				0.0200
Multifamily | Bridge loans | Interest Deferral, Extended Maturity, And Interest Forgiveness | Maximum
Financing Receivable, Modified [Line Items]
Variable rate, spread				4.30%
Percentage of interest foregone				0.0215
Office
Financing Receivable, Modified [Line Items]
Financing receivable, net of reserve				$ 37,100			37,100
Financing receivable, reserve for credit loss				8,000			$ 8,000
Loan reserve				$ 2,300