Income taxes - Changes in Uncertain Tax Positions (Detail) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2023	Jun. 30, 2022
Unrecognized tax benefits:
Deferred income tax expense benefit non cash	$ 1.0	$ 1.1
Lapse due to applicable statute of limitations	$ (0.2)

Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)(4)
-URI https://asc.fasb.org/extlink&oid=121826272&loc=SL6600010-109319

Name:	us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration