Segment reporting - Narrative (Details) $ in Thousands	3 Months Ended
Mar. 31, 2025 USD ($) segment	Mar. 31, 2024 USD ($)
Segment Reporting [Abstract]
Number of reportable segments \| segment	2
Segment reporting
Marketable securities income/(loss) and interest	$ 6,787	$ 6,611
Operating expenses	41,101	30,138
Finance costs	33,880	32,567
Foreign currency transactions (gains)/losses	(600)	492
Operating Segments
Segment reporting
Marketable securities income/(loss) and interest	6,700	6,518
Operating expenses	39,523	29,664
Finance costs	33,880	32,567
Foreign currency transactions (gains)/losses	(599)	488
Operating Segments \| Principal Finance
Segment reporting
Marketable securities income/(loss) and interest	6,700	6,518
Operating expenses	32,463	24,661
Finance costs	33,880	32,567
Foreign currency transactions (gains)/losses	(599)	488
Operating Segments \| Asset Management and Other Services
Segment reporting
Marketable securities income/(loss) and interest	0	0
Operating expenses	7,060	5,003
Finance costs	0	0
Foreign currency transactions (gains)/losses	$ 0	0
Operating Segments \| Revision of Prior Period, Adjustment \| Principal Finance
Segment reporting
Finance costs		600
Operating Segments \| Revision of Prior Period, Adjustment \| Principal Finance \| Reclassification, Corporate to Personal Finance
Segment reporting
Marketable securities income/(loss) and interest		6,500
Operating expenses		2,800
Finance costs		900
Foreign currency transactions (gains)/losses		500
Operating Segments \| Revision of Prior Period, Adjustment \| Asset Management and Other Services
Segment reporting
Finance costs		(600)
Operating Segments \| Revision of Prior Period, Adjustment \| Asset Management and Other Services \| Reclassification, Corporate to Asset Management and Other Services
Segment reporting
Operating expenses		2,900
Reconciling items \| Revision of Prior Period, Adjustment \| Reclassification, Corporate to Personal Finance
Segment reporting
Marketable securities income/(loss) and interest		(6,500)
Operating expenses		(2,800)
Finance costs		(900)
Foreign currency transactions (gains)/losses		500
Reconciling items \| Revision of Prior Period, Adjustment \| Reclassification, Corporate to Asset Management and Other Services
Segment reporting
Operating expenses		$ (2,900)

Marketable Security, Gain (Loss) And Interest Income

No definition available.

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- Definition

Amount, before tax, of realized and unrealized gain (loss) from foreign currency transaction.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(7))
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 830
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-Name Accounting Standards Codification
-Section 35
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482014/830-20-35-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 830
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-Name Accounting Standards Codification
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-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481956/830-20-45-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 830
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-Name Accounting Standards Codification
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 830
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481839/830-10-45-17

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- Definition

Amount of interest expense classified as nonoperating.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-22

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2

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- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 47
-Subparagraph (a)
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
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Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 280
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-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-18

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- Definition

Generally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services. Includes selling, general and administrative expense.

+ References

No definition available.

+ Details

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- References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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