Segment reporting - Group's Total Assets by Reporting Segments (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Segment reporting
Cash and cash equivalents and marketable securities	$ 570,183	$ 548,950
Other assets	65,774	61,006
Due from settlement of capital provision assets	102,648	183,858	$ 131,688	$ 265,540
Capital provision assets	5,305,021	5,243,917	$ 5,096,807	$ 5,045,388
Total assets	6,180,805	6,175,025
Operating Segments
Segment reporting
Cash and cash equivalents and marketable securities	548,208	520,681
Other assets	187,651	175,481
Due from settlement of capital provision assets	102,648	183,651
Capital provision assets	3,627,403	3,571,224
Total assets	4,603,089	4,588,331
Operating Segments \| Principal Finance
Segment reporting
Cash and cash equivalents and marketable securities	538,374	508,031
Other assets	26,911	23,711
Due from settlement of capital provision assets	102,648	183,651
Capital provision assets	3,627,403	3,571,224
Total assets	4,406,530	4,397,954
Operating Segments \| Asset Management and Other Services
Segment reporting
Cash and cash equivalents and marketable securities	9,834	12,650
Other assets	160,740	151,770
Due from settlement of capital provision assets	0	0
Capital provision assets	0	0
Total assets	196,560	190,377
Reconciling items
Segment reporting
Cash and cash equivalents and marketable securities	21,975	28,269
Other assets	(121,877)	(114,475)
Due from settlement of capital provision assets	0	207
Capital provision assets	1,677,618	1,672,693
Total assets	$ 1,577,716	$ 1,586,694