Fair value measurement - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Jun. 30, 2018	Aug. 04, 2018	Feb. 01, 2020
Fair Value Disclosures [Abstract]
Sale of receivables. percentage deferred until second anniversary	5.00%	5.00%
Deferred payment, fair value disclosure			$ 21.9