Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature, attributable to parent entity.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4569643-111683

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4569616-111683

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Summary of significant accounting policies - Comprehensive loss and Net loss per share (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summary of significant accounting policies
Foreign currency translation (loss)/gain		$ (0.9)	$ (2.4)	$ 1.8
Common stock
Summary of significant accounting policies
Shares issued upon conversion of redeemable convertible preferred stock (in shares)	14,582,161
Class A common stock
Summary of significant accounting policies
Shares issued upon conversion of redeemable convertible preferred stock (in shares)	3,819,732