Fair value measurements - Investments in Company-Sponsored Funds (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Summary of Investment Holdings [Line Items]
Fair Value	$ 5,518	$ 8,795
Unfunded Commitments	2,367	3,018
Hedge Funds
Summary of Investment Holdings [Line Items]
Fair Value	446	574
Unfunded Commitments	$ 0	$ 0
Hedge Funds | Minimum
Summary of Investment Holdings [Line Items]
Redemption notice period	30 days	30 days
Hedge Funds | Maximum
Summary of Investment Holdings [Line Items]
Redemption notice period	120 days	120 days
Private Equity Funds
Summary of Investment Holdings [Line Items]
Fair Value	$ 5,072	$ 8,221
Unfunded Commitments	$ 2,367	$ 3,018