CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 30, 2016	Jan. 31, 2016	Apr. 30, 2015	Jan. 31, 2015
Cash and Cash Equivalents
Weighted average annual interest rate on CDs (as a percent)	0.80%
Cash, cash equivalents	$ 191,430	$ 160,909	$ 274,528	$ 333,691
Joint Venture
Cash and Cash Equivalents
Cash, cash equivalents	48,100
Short-term investments	3,000
Held-to-maturity Securities
Cash and Cash Equivalents
Accrued interest on held-to-maturity securities	$ 200	$ 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