CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS - Additional Information (Details) - USD ($)	6 Months Ended
	Jul. 31, 2015	Jan. 31, 2015	Jul. 31, 2014	Jan. 31, 2014
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents	$ 182,136,000	$ 333,691,000	$ 345,158,000	$ 272,209,000
Joint Venture [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents	55,900,000
Short-term investments	40,000,000
Held-to-maturity Securities [Member]
Cash and Cash Equivalents [Line Items]
Accrued interest on held-to-maturity securities	$ 64,000
Held-to-maturity Securities [Member] | Minimum [Member]
Cash and Cash Equivalents [Line Items]
Maturity period	90 days
Held-to-maturity Securities [Member] | Maximum [Member]
Cash and Cash Equivalents [Line Items]
Maturity period	1 year