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CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS (Details) - USD ($)
$ in Millions
 6 Months Ended 12 Months Ended
Jul. 31, 2017
Jan. 31, 2017
Cash and Cash Equivalents    
Weighted average annual interest rate on short-term investment CDs (as a percent) 1.27% 1.13%
Held-to-maturity Securities    
Cash and Cash Equivalents    
Maturity period 252 days 185 days
Accrued interest on held-to-maturity securities $ 1.4 $ 0.8