Fair value measurements - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities owned, at fair value	$ 498,594	$ 634,504	[1]
Auction rate securities valuation adjustment	5,200
Investments	$ 7,068	12,970
Forward or delayed delivery of the underlying instrument with settlement	180 days
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities owned, at fair value	$ 79,166	51,414
Investments	7,068	12,970
Level 2 | Other Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	6,000
Auction rate securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities owned, at fair value	$ 31,776	31,804
Auction rate securities | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities owned, at fair value		$ 0

[1] (1) Certain prior period reported amounts were reclassified to conform to the current period presentation, See Note 2.