INCOME TAXES - Research and Development Tax Credits (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
INCOME TAXES
Period for identify and quantify the amounts of research and development credits	3 years
Income tax expense (benefits) associated with research and development activities	$ 16.6	$ 5.2	$ 10.9	$ 0.5
Effects on dilutive earnings per share, research and development activities	$ 1.06
Unrecognized income tax benefits related to research and development credits	$ 5.1
Unrecognized tax benefits related to research and development credits that would impact effective tax rate, if recognized	$ 2.2	$ 2.6	$ 0.3