Variable interest entities - Unconsolidated VIEs (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Variable Interest Entity [Line Items]
Carrying amount	$ 1,558,905	$ 1,600,718
Asset Management
Variable Interest Entity [Line Items]
Carrying amount	59,292	66,423
Insurance Solutions
Variable Interest Entity [Line Items]
Carrying amount	1,499,613	1,534,295
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Carrying amount	58,161	60,661
Maximum exposure to loss	59,574	62,074
Variable Interest Entity, Not Primary Beneficiary | Asset Management
Variable Interest Entity [Line Items]
Carrying amount	28,348	28,209
Maximum exposure to loss	29,761	29,622
Variable Interest Entity, Not Primary Beneficiary | Asset Management | Related Party
Variable Interest Entity [Line Items]
Carrying amount	28,348	28,209
Maximum exposure to loss	29,761	29,622
Variable Interest Entity, Not Primary Beneficiary | Insurance Solutions
Variable Interest Entity [Line Items]
Carrying amount	29,813	32,452
Maximum exposure to loss	29,813	32,452
Variable Interest Entity, Not Primary Beneficiary | Insurance Solutions | Nonrelated Party
Variable Interest Entity [Line Items]
Carrying amount	15,604	17,097
Maximum exposure to loss	15,604	17,097
Variable Interest Entity, Not Primary Beneficiary | Insurance Solutions | Related Party
Variable Interest Entity [Line Items]
Carrying amount	14,209	15,355
Maximum exposure to loss	$ 14,209	$ 15,355