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Income taxes - Narrative (Details) - USD ($)	12 Months Ended
Income taxes - Narrative (Details) - USD ($)	Dec. 31, 2025	Dec. 31, 2024	Dec. 06, 2023
Operating Loss Carryforwards [Line Items]
Less: valuation allowance	$ 28,537,000	$ 34,737,000
Uncertain tax position, interest and penalties expense	0	0
Subsidiaries
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	115,300,000	130,500,000
Capital Loss Carryforward
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	63,900,000	278,900,000
Capital Loss Carryforward \| Tax Year 2020
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	225,700,000
Western Asset Mortgage Capital Corporation
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	317,300,000	319,400,000	$ 321,600,000
Operating loss carryforwards, not subject to expiration			$ 223,800,000
Western Asset Mortgage Capital Corporation \| Capital Loss Carryforward
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	$ 153,900,000	$ 150,600,000