Commitments and contingencies - Future annual minimum rental payments (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
2020	$ 6.5
2021	8.1
2022	7.2
2023	4.7
2024	2.3
2025 and after	1.1
Total future annual minimum rental payments as at March 31, 2020	29.9
Less: present value discount	(2.1)
Lease liability	$ 27.8	$ 29.3

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Amount of lessee's undiscounted obligation for lease payments for operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918701-209980

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Amount of lessee's undiscounted obligation for lease payments for operating lease having an initial or remaining lease term in excess of one year due in remainder of fiscal year following latest fiscal year.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
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-SubTopic 20
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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