Summary of Business and Significant Accounting Policies - Schedule of Unaudited Condensed Consolidated Statements of Comprehensive Income (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended
Apr. 30, 2018
Apr. 30, 2017
Revenues:    
Subscription services $ 156,003 $ 129,131 [1]
Operating expenses:    
Sales and marketing [2] 34,385 30,141 [1]
Operating income 43,956 38,863 [1]
Provision for income taxes 1,785 2,458 [1]
Net income $ 44,310 $ 36,996 [1]
Net income per share attributable to Class A and Class B common stockholders:    
Basic $ 0.31 $ 0.27 [1]
Diluted $ 0.29 $ 0.24 [1]
As Reported [member] | Topic 606 [Member]    
Revenues:    
Subscription services   $ 127,277
Operating expenses:    
Sales and marketing   29,810
Operating income   37,339
Provision for income taxes   1,907
Net income   $ 36,023
Net income per share attributable to Class A and Class B common stockholders:    
Basic   $ 0.26
Diluted   $ 0.24
Adjustments [Member] | Topic 606 [Member]    
Revenues:    
Subscription services   $ 1,854
Operating expenses:    
Sales and marketing   331
Operating income   1,524
Provision for income taxes   551
Net income   $ 973
Net income per share attributable to Class A and Class B common stockholders:    
Basic   $ 0.01
[1] See note 1 of the notes to the condensed consolidated financial statements for a summary of adjustments.
[2] Includes stock-based compensation as follows:  Cost of revenues: Cost of subscription services $345 $342 Cost of professional services and other 2,328 1,689 Research and development 4,667 3,802 Sales and marketing 4,088 3,847 General and administrative 5,583 2,108 Total stock-based compensation $17,011 $11,788