Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 17.3	$ 10.1	$ 7.2
Gross increases – tax positions in prior period	6.3	8.0	3.2
Gross decreases – tax positions in prior period	(0.7)	0.0	(0.9)
Gross increases – tax positions in current period	1.9	1.3	0.6
Settlements	(5.2)	0.0	0.0
Lapse of statute of limitations	0.1	(2.1)	0.0
Unrecognized tax benefits at end of year	$ 19.7	$ 17.3	$ 10.1