Fair value measurements - Schedule of Investments in Company-Sponsored Funds (Details) - USD ($) $ in Thousands	6 Months Ended	9 Months Ended
	Jun. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 5,564,000		$ 5,373
Unfunded Commitments	790		1,314
Hedge Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	262,000		283
Unfunded Commitments	$ 0		0
Hedge Funds | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Redemption Notice Period	30 days	30 days
Hedge Funds | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Redemption Notice Period	120 days	120 days
Private Equity Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 5,302,000		5,090
Unfunded Commitments	$ 790		$ 1,314