CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS (Details) - USD ($) $ in Thousands	6 Months Ended
	Jul. 31, 2016	Jan. 31, 2016	Jul. 31, 2015	Jan. 31, 2015
Cash and Cash Equivalents
Weighted average annual interest rate on short-term investment CDs (as a percent)	0.81%
Cash, cash equivalents	$ 162,855	$ 160,909	$ 182,136	$ 333,691
Joint Venture
Cash and Cash Equivalents
Cash, cash equivalents	38,400
Held-to-maturity Securities
Cash and Cash Equivalents
Accrued interest on held-to-maturity securities	$ 300	$ 100
Held-to-maturity Securities | Minimum
Cash and Cash Equivalents
Maturity period	3 months
Held-to-maturity Securities | Maximum
Cash and Cash Equivalents
Maturity period	12 months