Loans and Investments - Loan Modifications (Details) $ in Thousands		1 Months Ended	3 Months Ended					6 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2024 USD ($) loan	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($) loan	Jun. 30, 2024 USD ($) loan	Mar. 31, 2024 USD ($) loan	Dec. 31, 2023 USD ($) loan	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) loan	Sep. 30, 2024 USD ($) loan	Dec. 31, 2023 USD ($) loan
Financing Receivable, Modified [Line Items]
Financing receivable, specific reserve			$ 1,000
Loans and investments, gross			11,565,538			$ 12,615,006			$ 11,565,538	$ 12,615,006
New borrower investments			$ 2,000	$ 4,900	$ 2,000
Rate cap strike price, percentage			5.25%
Total specific reserve			$ 3,500						$ 3,500
Number of impaired loans (less unearned revenue and other holdbacks and adjustments) by asset class | loan			27			19			27	19
Interest reserve									$ 200,400	$ 156,100
Future funding commitments, modified loans, borrowers experiencing financial difficulty			$ 49,000						$ 49,000
Number of loans modified not pursuant to contract | loan	8			8				8
Loans modified, not pursuant to contract, amount								$ 212,500
Loan modification, refinancing, and extensions | loan			0						0	0
Secondary Loan
Financing Receivable, Modified [Line Items]
Financing receivable, net of reserve	$ 4,400		$ 3,500	$ 4,400				4,400	$ 3,500
Loans modified in period, floor interest rate spread			0.0375	0.0375
Senior Lien
Financing Receivable, Modified [Line Items]
Financing receivable, basis spread on variable rate			0.0075	0.0050
Financing receivable, floor interest rate			0.0575	0.0600
Loans modified in period, floor interest rate spread			0.0300	0.0325
Senior Lien | Senior Position Loan
Financing Receivable, Modified [Line Items]
Financing receivable, net of reserve	32,000		$ 29,000	$ 32,000				32,000	29,000
Financial Asset, Greater Than 60 Days Past Due
Financing Receivable, Modified [Line Items]
Financing receivable, specific reserve				2,500
Loans and investments, gross	32,500			$ 32,500				$ 32,500
Financial Asset, 60 Days Past Due
Financing Receivable, Modified [Line Items]
Financing receivable, specific reserve						$ 5,000
Loans and investments, gross					36,400
Financing receivable, net of reserve						31,400				$ 31,400
Temporary Interest Rate Relief And Extended Maturity, Six Loans | Financial Asset, Greater Than 60 Days Past Due
Financing Receivable, Modified [Line Items]
Financing receivable, amount modified in period	118,900
Temporary Interest Rate Relief And Extended Maturity, Six Loans | Financial Asset, Less Than 60 Days Past Due
Financing Receivable, Modified [Line Items]
Financing receivable, amount modified in period	$ 87,500
Temporary Interest Rate Relief
Financing Receivable, Modified [Line Items]
Number of loans modified not pursuant to contract | loan	5			5				5
Loans modified, not pursuant to contract, amount								$ 123,200
Temporary Interest Rate Relief, Three Loans
Financing Receivable, Modified [Line Items]
Financing receivable, specific reserve				$ 19,200
Number of loans modified not pursuant to contract | loan	3			3				3
Loans modified, not pursuant to contract, amount				$ 81,000
Temporary Interest Rate Relief, Five Loans
Financing Receivable, Modified [Line Items]
Number of loans modified not pursuant to contract | loan	5			5				5
Loans modified, not pursuant to contract, amount				$ 131,500
Bridge loans
Financing Receivable, Modified [Line Items]
Financing receivable, fixed interest rate		0.0300	0.0700
Financing receivable, accrual rate		0.0300
Financing receivable, specific reserve					1,500
Loans and investments, gross			$ 11,169,284		$ 13,500	12,273,244	$ 70,500		$ 11,169,284	12,273,244
Loans modified in period, floor interest rate spread					0.0415
Variable rate, spread							3.40%
Fixed interest rate, first twenty four months					0.0825
Fixed interest rate, last twelve months					0.0850
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			6		16
Financing receivable, amount modified in period			$ 443,600		$ 692,800
Weighted average pay rate	0.0592			0.0730	0.0695
Financing receivable, accrual rate	0.0262			0.0204	0.0186
Loans previously classified as non-performing					$ 712,900
Multifamily | Bridge loans | Financial Asset, Greater Than 60 Days Past Due
Financing Receivable, Modified [Line Items]
Loans previously classified as non-performing					12,200
Multifamily | Bridge loans | Financial Asset, Less Than 60 Days Past Due
Financing Receivable, Modified [Line Items]
Loans previously classified as non-performing					$ 92,700
Multifamily | Bridge loans | Minimum
Financing Receivable, Modified [Line Items]
Financing receivable, basis spread on variable rate			0.0325
Variable rate, spread				3.25%	3.25%
Multifamily | Bridge loans | Maximum
Financing Receivable, Modified [Line Items]
Financing receivable, basis spread on variable rate			0.0485
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			17	14
Financing receivable, amount modified in period			$ 678,200	$ 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, Sixteen Loans
Financing Receivable, Modified [Line Items]
Number of financing receivables modified during the period | loan			16
Financing receivable, amount modified in period			$ 663,700
Multifamily | Bridge loans | Temporary Interest Rate Relief And Extended Maturity, One Loan
Financing Receivable, Modified [Line Items]
Number of financing receivables modified during the period | loan			1
Financing receivable, amount modified in period			$ 14,500
Multifamily | Bridge loans | Temporary Interest Rate Relief And Extended Maturity, Six Loans
Financing Receivable, Modified [Line Items]
Number of financing receivables modified during the period | loan	6
Financing receivable, amount modified in period	$ 341,900
Multifamily | Bridge loans | Temporary Interest Rate Relief And Extended Maturity, Two Loans
Financing Receivable, Modified [Line Items]
Number of financing receivables modified during the period | loan			2
Financing receivable, amount modified in period			$ 52,900
Financing receivable, specific reserve			$ 4,600
Multifamily | Bridge loans | Temporary Interest Rate Relief And Extended Maturity, Thirteen Loans
Financing Receivable, Modified [Line Items]
Number of financing receivables modified during the period | loan			13
Financing receivable, amount modified in period			$ 586,300
Multifamily | Bridge loans | Temporary Interest Rate Relief And Extended Maturity, Thirteen Loans | Minimum
Financing Receivable, Modified [Line Items]
Financing receivable modified, weighted average term increase from modification			12 months
Multifamily | Bridge loans | Temporary Interest Rate Relief And Extended Maturity, Thirteen Loans | Maximum
Financing Receivable, Modified [Line Items]
Financing receivable modified, weighted average term increase from modification			31 months
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			$ 206,800	$ 201,900
Financing receivable modified, weighted average term increase from modification			12 months
Number of financing receivables with extended maturities | loan			3	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 | 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 | 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
Financing receivable modified, weighted average term increase from modification						1 year
Variable rate, spread						4.25%
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