Fair value measurements - Schedule of Investments in Company-Sponsored Funds (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 5,027,000	$ 5,518
Unfunded Commitments	1,324,000	2,367
Hedge Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	341,000	446
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	$ 4,686,000	$ 5,072
Unfunded Commitments	$ 1,324,000	$ 2,367