Fair value measurement - Outstanding Debt (Details) - USD ($) $ in Millions	May 02, 2020	Feb. 01, 2020	May 04, 2019
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	$ 246.0	$ 245.9	$ 680.0
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	197.1	244.8	649.4
Senior Notes | Level 2 | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	146.5	146.4	395.5
Senior Notes | Level 2 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	97.1	144.8	363.4
Term Loan | Level 2 | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	99.5	99.5	284.5
Term Loan | Level 2 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt	$ 100.0	$ 100.0	$ 286.0