Fair value measurements - Schedule of Valuation Techniques (Details) $ in Thousands	Sep. 30, 2024 USD ($) quote	Dec. 31, 2023 USD ($) quote
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 197,558	$ 162,821
Derivative assets, at fair value	5,341	10,605
Derivative Liability	(111)	(70)
Legacy WMC CMBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	52,685	56,349
Legacy WMC Other Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	998	1,156
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative assets, at fair value	149	1,172
Level 3 | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative assets, at fair value	149	1,172
Derivative Liability	$ (25)	$ (7)
Level 3 | Yield | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.0604	0.0629
Derivative liability, measurement input	0.0604	0.0647
Level 3 | Yield | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.0734	0.0832
Derivative liability, measurement input	0.0654	0.0700
Level 3 | Yield | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.0623	0.0681
Derivative liability, measurement input	0.0606	0.0651
Level 3 | Projected Collateral Prepayments | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.1269	0.1820
Derivative liability, measurement input	0.1691	0.2736
Level 3 | Projected Collateral Prepayments | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.2858	0.3378
Derivative liability, measurement input	0.2725	0.3444
Level 3 | Projected Collateral Prepayments | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.2161	0.2700
Derivative liability, measurement input	0.2409	0.3430
Level 3 | Projected Collateral Losses | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.0002	0.0000
Derivative liability, measurement input	0.0001	0.0000
Level 3 | Projected Collateral Losses | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.0347	0.0082
Derivative liability, measurement input	0.0166	0.0002
Level 3 | Projected Collateral Losses | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.0088	0.0014
Derivative liability, measurement input	0.0009	0.0000
Level 3 | Projected Collateral Severities | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.1000	0.1000
Derivative liability, measurement input	0.1000	0.1000
Level 3 | Projected Collateral Severities | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.1000	0.1000
Derivative liability, measurement input	0.1000	0.1000
Level 3 | Projected Collateral Severities | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.1000	0.1000
Derivative liability, measurement input	0.1000	0.1000
Level 3 | Pull Through Percentages | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.6000	0.6000
Derivative liability, measurement input	0.6000	0.6000
Level 3 | Pull Through Percentages | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	1.0000	1.0000
Derivative liability, measurement input	1.0000	1.0000
Level 3 | Pull Through Percentages | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.7429	0.9221
Derivative liability, measurement input	0.7597	0.9922
Level 3 | Residential Mortgage | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, fair value	$ 263,080	$ 316,854
Level 3 | Residential Mortgage | Securitized Residential Mortgage Loans | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, fair value	$ 6,226,698	$ 5,358,281
Level 3 | Residential Mortgage | Yield | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0581	0.0613
Level 3 | Residential Mortgage | Yield | Minimum | Securitized Residential Mortgage Loans | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0521	0.0567
Level 3 | Residential Mortgage | Yield | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.1255	0.1875
Level 3 | Residential Mortgage | Yield | Maximum | Securitized Residential Mortgage Loans | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.1015	0.0947
Level 3 | Residential Mortgage | Yield | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0785	0.0664
Level 3 | Residential Mortgage | Yield | Weighted Average | Securitized Residential Mortgage Loans | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0571	0.0623
Level 3 | Residential Mortgage | Projected Collateral Prepayments | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0571	0.0389
Level 3 | Residential Mortgage | Projected Collateral Prepayments | Minimum | Securitized Residential Mortgage Loans | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0413	0.0302
Level 3 | Residential Mortgage | Projected Collateral Prepayments | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.3275	0.3435
Level 3 | Residential Mortgage | Projected Collateral Prepayments | Maximum | Securitized Residential Mortgage Loans | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.1100	0.1047
Level 3 | Residential Mortgage | Projected Collateral Prepayments | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.2019	0.2488
Level 3 | Residential Mortgage | Projected Collateral Prepayments | Weighted Average | Securitized Residential Mortgage Loans | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0626	0.0472
Level 3 | Residential Mortgage | Projected Collateral Losses | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0000	0.0000
Level 3 | Residential Mortgage | Projected Collateral Losses | Minimum | Securitized Residential Mortgage Loans | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0002	0.0002
Level 3 | Residential Mortgage | Projected Collateral Losses | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.2516	0.1272
Level 3 | Residential Mortgage | Projected Collateral Losses | Maximum | Securitized Residential Mortgage Loans | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0195	0.0188
Level 3 | Residential Mortgage | Projected Collateral Losses | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0117	0.0015
Level 3 | Residential Mortgage | Projected Collateral Losses | Weighted Average | Securitized Residential Mortgage Loans | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0015	0.0016
Level 3 | Residential Mortgage | Projected Collateral Severities | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	(0.2500)	(0.3875)
Level 3 | Residential Mortgage | Projected Collateral Severities | Minimum | Securitized Residential Mortgage Loans | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	(0.1327)	(0.1344)
Level 3 | Residential Mortgage | Projected Collateral Severities | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.5540	0.4401
Level 3 | Residential Mortgage | Projected Collateral Severities | Maximum | Securitized Residential Mortgage Loans | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.2600	0.2600
Level 3 | Residential Mortgage | Projected Collateral Severities | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.1735	0.0962
Level 3 | Residential Mortgage | Projected Collateral Severities | Weighted Average | Securitized Residential Mortgage Loans | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.1899	0.1738
Level 3 | Legacy WMC Commercial Loans | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, fair value	$ 66,875	$ 66,303
Level 3 | Legacy WMC Commercial Loans | Yield | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0764	0.0816
Level 3 | Legacy WMC Commercial Loans | Yield | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0944	0.1013
Level 3 | Legacy WMC Commercial Loans | Yield | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0885	0.0947
Level 3 | Legacy WMC Commercial Loans | Credit Spread | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0377	0.0377
Level 3 | Legacy WMC Commercial Loans | Credit Spread | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0517	0.0556
Level 3 | Legacy WMC Commercial Loans | Credit Spread | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.0471	0.0496
Level 3 | Legacy WMC Commercial Loans | Recovery Percentage | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	1.0000	1.0000
Level 3 | Legacy WMC Commercial Loans | Recovery Percentage | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	1.0000	1.0000
Level 3 | Legacy WMC Commercial Loans | Recovery Percentage | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	1.0000	1.0000
Level 3 | Legacy WMC Commercial Loans | Loan-to-Value | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.4250	0.4250
Level 3 | Legacy WMC Commercial Loans | Loan-to-Value | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.7722	0.7722
Level 3 | Legacy WMC Commercial Loans | Loan-to-Value | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.6368	0.6361
Level 3 | Non-Agency RMBS | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 111,171	$ 37,533
Level 3 | Non-Agency RMBS | Yield | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0537	0.0623
Level 3 | Non-Agency RMBS | Yield | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.3500	0.1400
Level 3 | Non-Agency RMBS | Yield | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0732	0.0970
Level 3 | Non-Agency RMBS | Projected Collateral Prepayments | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0460	0.0455
Level 3 | Non-Agency RMBS | Projected Collateral Prepayments | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.1275	0.0526
Level 3 | Non-Agency RMBS | Projected Collateral Prepayments | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0894	0.0493
Level 3 | Non-Agency RMBS | Projected Collateral Losses | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0001	0.0017
Level 3 | Non-Agency RMBS | Projected Collateral Losses | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0041	0.0028
Level 3 | Non-Agency RMBS | Projected Collateral Losses | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0012	0.0025
Level 3 | Non-Agency RMBS | Projected Collateral Severities | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.1000	0.1000
Level 3 | Non-Agency RMBS | Projected Collateral Severities | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.2500	0.1000
Level 3 | Non-Agency RMBS | Projected Collateral Severities | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.1948	0.1000
Level 3 | Legacy WMC CMBS | Consensus Pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 636	$ 5,796
Level 3 | Legacy WMC CMBS | Offered Quotes | Minimum | Consensus Pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input | quote	6.06	55.20
Level 3 | Legacy WMC CMBS | Offered Quotes | Maximum | Consensus Pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input | quote	6.06	55.20
Level 3 | Legacy WMC CMBS | Offered Quotes | Weighted Average | Consensus Pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input | quote	6.06	55.20
Level 3 | Legacy WMC Other Securities | Consensus Pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 998	$ 1,156
Level 3 | Legacy WMC Other Securities | Offered Quotes | Minimum | Consensus Pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input | quote	5,883.06	6,821.32
Level 3 | Legacy WMC Other Securities | Offered Quotes | Maximum | Consensus Pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input | quote	5,883.06	6,821.32
Level 3 | Legacy WMC Other Securities | Offered Quotes | Weighted Average | Consensus Pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input | quote	5,883.06	6,821.32
Level 3 | AG Arc | Comparable Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, fair value	$ 30,967	$ 33,574
Level 3 | AG Arc | Book Value Multiple | Minimum | Comparable Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.95	0.89
Level 3 | AG Arc | Book Value Multiple | Maximum | Comparable Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.95	0.89
Level 3 | AG Arc | Book Value Multiple | Weighted Average | Comparable Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale, measurement input	0.95	0.89
Level 3 | Securitized Debt | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt, fair value	$ (5,497,552)	$ (4,711,623)
Level 3 | Securitized Debt | Yield | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt, measurement input	0.0443	0.0492
Level 3 | Securitized Debt | Yield | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt, measurement input	0.2500	0.1500
Level 3 | Securitized Debt | Yield | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt, measurement input	0.0528	0.0572
Level 3 | Securitized Debt | Projected Collateral Prepayments | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt, measurement input	0.0413	0.0302
Level 3 | Securitized Debt | Projected Collateral Prepayments | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt, measurement input	0.1100	0.1047
Level 3 | Securitized Debt | Projected Collateral Prepayments | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt, measurement input	0.0622	0.0466
Level 3 | Securitized Debt | Projected Collateral Losses | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt, measurement input	0.0002	0.0002
Level 3 | Securitized Debt | Projected Collateral Losses | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt, measurement input	0.0050	0.0040
Level 3 | Securitized Debt | Projected Collateral Losses | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt, measurement input	0.0014	0.0015
Level 3 | Securitized Debt | Projected Collateral Severities | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt, measurement input	0.1000	0.0371
Level 3 | Securitized Debt | Projected Collateral Severities | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt, measurement input	0.2600	0.2600
Level 3 | Securitized Debt | Projected Collateral Severities | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Long-term debt, measurement input	0.1929	0.1776