Segment reporting - Group's Total Assets by Reporting Segments (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Mar. 31, 2026	Dec. 31, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024
Segment reporting
Cash and cash equivalents and marketable securities	$ 747,260		$ 655,923
Other assets	82,042		73,743
Due from settlement of capital provision assets	122,370	$ 180,041	164,804	$ 118,451	$ 102,648	$ 183,858
Capital provision assets	3,184,677	$ 3,120,499	5,609,949	$ 5,544,683	$ 5,305,021	$ 5,243,917
Total assets	4,272,138		6,641,172
Operating Segments
Segment reporting
Cash and cash equivalents and marketable securities	732,855		620,677
Other assets	211,487		191,657
Due from settlement of capital provision assets	122,370		164,804
Capital provision assets	2,319,497		3,912,194
Total assets	3,521,998		5,026,085
Operating Segments \| Principal Finance
Segment reporting
Cash and cash equivalents and marketable securities	716,636		599,011
Other assets	33,009		24,348
Due from settlement of capital provision assets	122,370		164,804
Capital provision assets	2,319,497		3,912,194
Total assets	3,302,299		4,811,081
Operating Segments \| Asset Management and Other Services
Segment reporting
Cash and cash equivalents and marketable securities	16,219		21,666
Other assets	178,478		167,309
Due from settlement of capital provision assets	0		0
Capital provision assets	0		0
Total assets	219,699		215,004
Reconciling items
Segment reporting
Cash and cash equivalents and marketable securities	14,405		35,246
Other assets	(129,445)		(117,914)
Due from settlement of capital provision assets	0		0
Capital provision assets	865,180		1,697,755
Total assets	$ 750,140		$ 1,615,087