Fair Value Measurements - Fair Value Hierarchy for Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jan. 31, 2016	Jan. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 214,024	$ 268,620
Corporate notes and bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	38,327	45,989
U.S. agency obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	124,586	199,911
Asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	5,454	9,319
Commercial paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	5,970	3,394
U.S. treasury securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	39,687	10,007
Fair value, measurements recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	256,509	314,076
Fair value, measurements recurring [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	28,087	41,861
Fair value, measurements recurring [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	228,422	272,215
Fair value, measurements recurring [Member] | Money market funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	28,087	41,861
Fair value, measurements recurring [Member] | Money market funds [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	28,087	41,861
Fair value, measurements recurring [Member] | Corporate notes and bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	11,396
Short-term investments	38,327	45,989
Fair value, measurements recurring [Member] | Corporate notes and bonds [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	11,396
Short-term investments	38,327	45,989
Fair value, measurements recurring [Member] | U.S. agency obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	3,002	3,595
Short-term investments	124,586	199,911
Fair value, measurements recurring [Member] | U.S. agency obligations [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	3,002	3,595
Short-term investments	124,586	199,911
Fair value, measurements recurring [Member] | Asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	5,454	9,319
Fair value, measurements recurring [Member] | Asset-backed securities [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	5,454	9,319
Fair value, measurements recurring [Member] | Commercial paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	5,970	3,394
Fair value, measurements recurring [Member] | Commercial paper [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	5,970	3,394
Fair value, measurements recurring [Member] | U.S. treasury securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	39,687	10,007
Fair value, measurements recurring [Member] | U.S. treasury securities [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 39,687	$ 10,007