Fair Value of Financial Instruments - Estimated Fair Value and Carrying Value of 2019 and 2020 Notes (Detail) - USD ($) $ in Thousands	Oct. 31, 2015	Jan. 31, 2015
Convertible Senior Notes Due 2019 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Convertible senior notes, Carrying Value	$ 297,349	$ 287,487
Convertible Senior Notes Due 2019 [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Convertible senior notes, Fair Value	268,898	$ 260,444
Convertible Senior Notes Due 2020 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Convertible senior notes, Carrying Value	221,288
Convertible Senior Notes Due 2020 [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Convertible senior notes, Fair Value	$ 210,597