Fair Value of Financial Instruments - Schedule of Assets Measured at Fair Value (Detail) - USD ($)	Feb. 03, 2018	Jan. 28, 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total cash equivalents		$ 8,003,000
Total		183,892,000
Money market funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total cash equivalents		2,510,000
Commercial paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total cash equivalents		5,493,000
Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total cash equivalents		2,510,000
Total		5,063,000
Level 1 [Member] | Money market funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total cash equivalents		2,510,000
Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total cash equivalents		5,493,000
Total		178,829,000
Level 2 [Member] | Commercial paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total cash equivalents		5,493,000
Short-term investments [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total investments	$ 0	142,677,000
Short-term investments [Member] | Commercial paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total investments		34,534,000
Short-term investments [Member] | Government agency obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total investments		108,143,000
Short-term investments [Member] | Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total investments		2,553,000
Short-term investments [Member] | Level 1 [Member] | Government agency obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total investments		2,553,000
Short-term investments [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total investments		140,124,000
Short-term investments [Member] | Level 2 [Member] | Commercial paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total investments		34,534,000
Short-term investments [Member] | Level 2 [Member] | Government agency obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total investments		105,590,000
Long-term investments [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total investments	$ 0	33,212,000
Long-term investments [Member] | Government agency obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total investments		33,212,000
Long-term investments [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total investments		33,212,000
Long-term investments [Member] | Level 2 [Member] | Government agency obligations [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total investments		$ 33,212,000