Fair value measurements - Schedule of Fair Value Measurement Inputs and Valuation Techniques (Details) $ in Thousands	Mar. 31, 2026 USD ($)	Dec. 31, 2025 USD ($)	Mar. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Financial assets
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 323,931	$ 282,270	$ 282,590	$ 257,265
Variable Interest Entity, Primary Beneficiary
Financial assets
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	130,310	120,680
Consolidated Balance Including Variable Interest Entity
Financial assets
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	317,220	275,701	277,218	256,766
Asset Management
Financial assets
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	6,711	6,569	5,372	499
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total financial liabilities			503	1,471
Insurance Solutions
Financial assets
Debt securities:	397,302	405,621
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	186,910	155,021	$ 144,825	$ 130,868
Insurance Solutions | Asset and mortgage-backed securities
Financial assets
Debt securities:	222,116	221,524
Insurance Solutions | Corporate
Financial assets
Debt securities:	158,528	166,693
Insurance Solutions | Consolidated Balance Including Variable Interest Entity
Financial assets
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	317,220	275,701
Enterprise value | Asset Management
Financial assets
Equity securities	6,565	6,409
Enterprise value | Insurance Solutions
Financial assets
Equity securities	289	$ 210
Enterprise value | Insurance Solutions | Variable Interest Entity, Primary Beneficiary
Financial assets
Equity securities	$ 1,140
Enterprise value | Enterprise Value, Multiple | Asset Management | Minimum
Financial assets
Equity securities, measurement input	12.5	12.5
Enterprise value | Enterprise Value, Multiple | Asset Management | Maximum
Financial assets
Equity securities, measurement input	13.5	13.5
Enterprise value | Enterprise Value, Multiple | Asset Management | Weighted Average
Financial assets
Equity securities, measurement input	13	13.0
Enterprise value | Enterprise Value, Multiple | Insurance Solutions | Minimum
Financial assets
Equity securities, measurement input	0.086	0.6
Enterprise value | Enterprise Value, Multiple | Insurance Solutions | Maximum
Financial assets
Equity securities, measurement input	0.086	0.6
Enterprise value | Enterprise Value, Multiple | Insurance Solutions | Weighted Average
Financial assets
Equity securities, measurement input	0.086	0.6
Enterprise value | Enterprise Value, Multiple | Insurance Solutions | Variable Interest Entity, Primary Beneficiary | Minimum
Financial assets
Equity securities, measurement input	1.8
Enterprise value | Enterprise Value, Multiple | Insurance Solutions | Variable Interest Entity, Primary Beneficiary | Maximum
Financial assets
Equity securities, measurement input	10.1
Enterprise value | Enterprise Value, Multiple | Insurance Solutions | Variable Interest Entity, Primary Beneficiary | Weighted Average
Financial assets
Equity securities, measurement input	6.0
Market approach | Asset Management
Financial assets
Equity securities	$ 75	$ 75
Probability-Weighted Expected Return Method | Asset Management
Financial assets
Other invested assets	$ 71	$ 72
Probability-Weighted Expected Return Method | Independent probabilities | Asset Management | Minimum
Financial assets
Equity securities, measurement input		0.050
Other invested assets , measurement input	5.00%
Probability-Weighted Expected Return Method | Independent probabilities | Asset Management | Maximum
Financial assets
Equity securities, measurement input		0.050
Other invested assets , measurement input	5.00%
Probability-Weighted Expected Return Method | Independent probabilities | Asset Management | Weighted Average
Financial assets
Equity securities, measurement input		0.050
Other invested assets , measurement input	5.00%
Probability-Weighted Expected Return Method | Dependent probabilities | Asset Management | Minimum
Financial assets
Equity securities, measurement input		0.024
Other invested assets , measurement input	2.40%
Probability-Weighted Expected Return Method | Dependent probabilities | Asset Management | Maximum
Financial assets
Equity securities, measurement input		0.037
Other invested assets , measurement input	3.70%
Probability-Weighted Expected Return Method | Dependent probabilities | Asset Management | Weighted Average
Financial assets
Equity securities, measurement input		0.031
Other invested assets , measurement input	3.10%
Probability-Weighted Expected Return Method Years To Cash Flows | Years to exit | Asset Management | Minimum
Financial assets
Equity securities, measurement input		2.5
Probability-Weighted Expected Return Method Years To Cash Flows | Years to exit | Asset Management | Maximum
Financial assets
Equity securities, measurement input		4.5
Probability-Weighted Expected Return Method Years To Cash Flows | Years to exit | Asset Management | Weighted Average
Financial assets
Equity securities, measurement input		3.5
Discounted cash flow
Financial assets
Other invested assets	$ 5,145
Discounted cash flow | Insurance Solutions
Financial assets
Equity securities	3,000	$ 3,000
Corporate loans	121,958	116,568
Other invested assets		5,637
Discounted cash flow | Insurance Solutions | Asset and mortgage-backed securities
Financial assets
Debt securities:	41,280	19,427
Discounted cash flow | Insurance Solutions | Corporate
Financial assets
Debt securities:	15,208	10,149
Discounted cash flow | Insurance Solutions | Variable Interest Entity, Primary Beneficiary
Financial assets
Equity securities		949
Corporate loans	$ 95,500	$ 89,608
Discounted cash flow | Discount rate | Insurance Solutions | Minimum
Financial assets
Equity securities, measurement input	0.058	0.056
Corporate loans, measurement input	0.000	0.000
Other invested assets , measurement input	7.50%	9.60%
Discounted cash flow | Discount rate | Insurance Solutions | Minimum | Asset and mortgage-backed securities
Financial assets
Debt securities, measurement input	0.063	0.063
Discounted cash flow | Discount rate | Insurance Solutions | Minimum | Corporate
Financial assets
Debt securities, measurement input	0.064	0.074
Discounted cash flow | Discount rate | Insurance Solutions | Maximum
Financial assets
Equity securities, measurement input	0.058	0.056
Corporate loans, measurement input	0.157	0.157
Other invested assets , measurement input	18.90%	19.70%
Discounted cash flow | Discount rate | Insurance Solutions | Maximum | Asset and mortgage-backed securities
Financial assets
Debt securities, measurement input	0.102	0.085
Discounted cash flow | Discount rate | Insurance Solutions | Maximum | Corporate
Financial assets
Debt securities, measurement input	0.080	0.089
Discounted cash flow | Discount rate | Insurance Solutions | Weighted Average
Financial assets
Equity securities, measurement input	0.058	0.056
Corporate loans, measurement input	0.082	0.082
Other invested assets , measurement input	17.00%	16.90%
Discounted cash flow | Discount rate | Insurance Solutions | Weighted Average | Asset and mortgage-backed securities
Financial assets
Debt securities, measurement input	0.090	0.076
Discounted cash flow | Discount rate | Insurance Solutions | Weighted Average | Corporate
Financial assets
Debt securities, measurement input	0.073	0.081
Discounted cash flow | Discount rate | Insurance Solutions | Variable Interest Entity, Primary Beneficiary | Minimum
Financial assets
Equity securities, measurement input		10.0
Corporate loans, measurement input	0.068	0.053
Discounted cash flow | Discount rate | Insurance Solutions | Variable Interest Entity, Primary Beneficiary | Maximum
Financial assets
Equity securities, measurement input		16.0
Corporate loans, measurement input	0.236	0.148
Discounted cash flow | Discount rate | Insurance Solutions | Variable Interest Entity, Primary Beneficiary | Weighted Average
Financial assets
Equity securities, measurement input		13.0
Corporate loans, measurement input	0.105	0.096
Recent transaction | Insurance Solutions
Financial assets
Equity securities	$ 30	$ 30
Recent transaction | Insurance Solutions | Variable Interest Entity, Primary Beneficiary
Financial assets
Corporate loans	$ 33,670	30,123
0 | Asset Management
Financial assets
Equity securities		$ 13
0 | Valuation Technique, Volatility | Asset Management | Minimum
Financial assets
Equity securities, measurement input		1.162
0 | Valuation Technique, Volatility | Asset Management | Maximum
Financial assets
Equity securities, measurement input		1.262
0 | Valuation Technique, Volatility | Asset Management | Weighted Average
Financial assets
Equity securities, measurement input		1.212
Option Pricing Model Years To Exercise | Valuation Technique, Years To Exercise | Asset Management | Minimum
Financial assets
Equity securities, measurement input		0.1
Option Pricing Model Years To Exercise | Valuation Technique, Years To Exercise | Asset Management | Maximum
Financial assets
Equity securities, measurement input		0.3
Option Pricing Model Years To Exercise | Valuation Technique, Years To Exercise | Asset Management | Weighted Average
Financial assets
Equity securities, measurement input		0.2