Fair value measurements - Schedule of Level 3 Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 282,270	$ 257,265
Purchases	36,196	25,723
Sales and repayments	(25,030)	(12,491)
Net realized gain (loss)	(703)	60
Included in income	(2,907)	281
Included in OCI	1,281	(101)
Transfer in	32,824	11,853
Ending Balance	323,931	282,590
Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held	(3,145)	(48)
Change in unrealized gains (losses) included in OCI on Level 3 assets and liabilities still held	$ 1,281	$ (101)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Recurring Basis Unobservable Input Reconciliation Asset Gain Loss Statement Of Income Extensible List Not Disclosed Flag	Included in income
Fair Value Asset Recurring Basis Still Held Unrealized Gain Loss Statement Of Income Extensible List Not Disclosed Flag		Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held
Variable Interest Entity, Primary Beneficiary
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 120,680
Ending Balance	130,310
Consolidated Balance Including Variable Interest Entity
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	275,701	$ 256,766
Purchases	36,196	20,723
Sales and repayments	(25,016)	(12,491)
Net realized gain (loss)	(706)	60
Included in income	(3,060)	408
Included in OCI	1,281	(101)
Transfer in	32,824	11,853
Ending Balance	317,220	277,218
Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held	(3,298)	79
Change in unrealized gains (losses) included in OCI on Level 3 assets and liabilities still held	1,281	$ (101)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Recurring Basis Unobservable Input Reconciliation Asset Gain Loss Statement Of Other Comprehensive Income Extensible List Not Disclosed Flag		Included in OCI
Asset Management
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	6,569	$ 499
Purchases	0	5,000
Sales and repayments	(14)
Net realized gain (loss)	3
Included in income	153	(127)
Ending Balance	6,711	5,372
Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held	$ 153	(127)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		1,471
Net realized gain (loss)		0
Included in income		(968)
Ending Balance		503
Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held		968
Fair Value Recurring Basis Unobservable Input Reconciliation Liability Gain Loss Statement Of Income Extensible List Not Disclosed Flag	Included in income
Asset Management | Debt obligations
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		1,471
Net realized gain (loss)		0
Included in income		(968)
Ending Balance		503
Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held		968
Asset Management | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 6,484	499
Purchases	0	5,000
Sales and repayments	0
Included in income	156	(127)
Ending Balance	6,640	5,372
Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held	156	(127)
Asset Management | Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	13
Purchases	0
Sales and repayments	(14)
Net realized gain (loss)	3
Included in income	(2)
Ending Balance	0
Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held	(2)
Asset Management | Other invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	72
Purchases	0
Included in income	(1)
Ending Balance	71
Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held	(1)
Insurance Solutions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	155,021	130,868
Purchases	828	2,851
Sales and repayments	(2,737)	(1,074)
Net realized gain (loss)	0	0
Included in income	(307)	428
Included in OCI	1,281	(101)
Transfer in	32,824	11,853
Ending Balance	186,910	144,825
Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held	(327)	405
Change in unrealized gains (losses) included in OCI on Level 3 assets and liabilities still held	1,281	(101)
Insurance Solutions | Consolidated Balance Including Variable Interest Entity
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	275,701
Ending Balance	317,220
Insurance Solutions | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	3,240	2,918
Sales and repayments		0
Included in income	79	13
Transfer in	0
Ending Balance	3,319	2,931
Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held	79	13
Insurance Solutions | Equity securities | Variable Interest Entity, Primary Beneficiary
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	949	141
Purchases	493	0
Sales and repayments	0	0
Net realized gain (loss)	0	0
Included in income	(302)	0
Ending Balance	1,140	141
Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held	(302)	0
Insurance Solutions | Other invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	5,637	4,575
Purchases	39
Sales and repayments	0	0
Net realized gain (loss)	0	0
Included in income	(7)	(370)
Included in OCI	(576)	(198)
Transfer in	52
Ending Balance	5,145	4,007
Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held	(6)	(390)
Change in unrealized gains (losses) included in OCI on Level 3 assets and liabilities still held	(576)	(198)
Insurance Solutions | Corporate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	10,149
Included in OCI	59	39
Transfer in	5,000	5,000
Ending Balance	15,208	5,039
Change in unrealized gains (losses) included in OCI on Level 3 assets and liabilities still held	59	39
Insurance Solutions | Asset and mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	19,427	8,641
Purchases	0
Sales and repayments	(212)	(228)
Included in income	(5)	(1)
Included in OCI	1,798	58
Transfer in	20,272	6,853
Ending Balance	41,280	15,323
Change in unrealized gains (losses) included in OCI on Level 3 assets and liabilities still held	1,798	58
Insurance Solutions | Corporate loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	116,568	114,734
Purchases	789	2,851
Sales and repayments	(2,525)	(846)
Net realized gain (loss)	0	0
Included in income	(374)	786
Transfer in	7,500	0
Ending Balance	121,958	117,525
Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held	(400)	782
Insurance Solutions | Corporate loans | Variable Interest Entity, Primary Beneficiary
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	119,731	125,757
Purchases	34,875	17,872
Sales and repayments	(22,279)	(11,417)
Net realized gain (loss)	(706)	60
Included in income	(2,451)	(20)
Ending Balance	129,170	132,252
Change in unrealized gains (losses) included in income on Level 3 assets and liabilities still held	$ (2,669)	$ (326)