Supplemental financial statement information (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019	Jan. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Depreciation expense	$ 4.0	$ 3.6	$ 12.0	$ 5.4
Remaining performance obligation	7.0		$ 7.0		$ 3.7
Deferred revenue interchange arrangement recognition term			10 years
Revenue recognition	$ 0.4		$ 2.2