Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Fair Value of Stock Options Granted (Detail)

v3.8.0.1
Stockholders' Equity - Fair Value of Stock Options Granted (Detail)
12 Months Ended
Jan. 31, 2018
Jan. 31, 2017
Jan. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility (range), Minimum 39.00% 40.00% 40.00%
Expected volatility (range), Maximum 46.00% 45.00% 45.00%
Weighted average volatility 41.00% 42.00% 42.00%
Weighted average interest rate 2.40% 1.10% 1.60%
Expected dividend yield 0.00% 0.00% 0.00%
Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term (in years) 6 years 6 years 6 years
Risk-free interest rate 1.90% 1.00% 1.50%
Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term (in years) 7 years 7 years 7 years
Risk-free interest rate 2.50% 2.00% 2.00%