Cash, Cash Equivalents and Short Term Investments - Additional Information (Detail) (USD $)	3 Months Ended
	Apr. 30, 2015	Jan. 31, 2015	Apr. 30, 2014	Jan. 31, 2014
Cash and Cash Equivalents [Line Items]
Liquid investments, original maturities	Three months or less
Short-term investments, maturity period	August to October 2015
Accrued interest on held-to-maturity securities	$ 17,000
Cash, cash equivalents	274,528,000	333,691,000	313,761,000	272,209,000
Short-term investments	56,017,000
Joint Venture [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents	105,300,000
Short-term investments	$ 24,000,000