Income taxes - Net tax payments (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income taxes
U.S. federal	$ 27.2	$ 25.2	$ 21.0
State	0.4	0.4	0.8
Income Taxes Paid, Net, Total	52.1	41.8	27.4
Norway
Income taxes
Non-U.S.	23.3	14.7	11.6
Germany
Income taxes
Non-U.S.	(1.1)	0.2	(5.5)
Other
Income taxes
Non-U.S.	$ 2.3	$ 1.3	$ (0.5)

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.

Name:	us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after income tax refund received, of cash paid to federal (national) tax jurisdiction for tax on income.

+ References

+ Details

Name:	us-gaap_IncomeTaxPaidFederalAfterRefundReceived
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, after income tax refund received, of cash paid to foreign tax jurisdiction for tax on income.

+ References

+ Details

Name:	us-gaap_IncomeTaxPaidForeignAfterRefundReceived
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, after income tax refund received, of cash paid to state and local tax jurisdictions for tax on income.

+ References

+ Details

Name:	us-gaap_IncomeTaxPaidStateAndLocalAfterRefundReceived
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, after refund, of cash paid to foreign, federal, state, and local jurisdictions as income tax.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482913/230-10-50-2A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 23
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-23

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-22

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482913/230-10-50-2

+ Details

Name:	us-gaap_IncomeTaxesPaidNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_IncomeTaxAuthorityAxis=country_NO
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeTaxAuthorityAxis=country_DE
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeTaxAuthorityAxis=us-gaap_ForeignTaxJurisdictionOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: