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CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS (Details) - Held-to-maturity Securities - USD ($)
$ in Millions
 12 Months Ended
Jan. 31, 2018
Jan. 31, 2017
Cash and Cash Equivalents    
Maturity period 293 days 185 days
Accrued interest on held-to-maturity securities $ 1.9 $ 0.8
Weighted average annual interest rates on short-term investment CDs (as a percent) 1.50% 1.10%