CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2014
Cash and Cash Equivalents
Weighted average annual interest rates on short-term investment CDs (as a percent)	1.13%	0.63%
Cash, cash equivalents	$ 167,198	$ 160,909	$ 333,691	$ 272,209
Joint Venture
Cash and Cash Equivalents
Cash, cash equivalents	$ 12,500
Held-to-maturity Securities
Cash and Cash Equivalents
Maturity period	185 days	174 days
Accrued interest on held-to-maturity securities	$ 100	$ 800