Summary of Business and Significant Accounting Policies - Schedule of Consolidated Statements of Comprehensive Income (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
		Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Revenues:
Subscription services										$ 554,446	$ 434,316	$ 316,314
Operating expenses:
Sales and marketing	[1]									130,898	116,803	80,984
Operating income		$ 34,887	$ 41,668	$ 36,898	$ 37,339	$ 32,530	$ 33,810	$ 23,822	$ 17,806	150,792	107,968	78,589
Net income		$ 33,706	$ 34,393	$ 37,844	$ 36,023	$ 21,707	$ 21,630	$ 12,958	$ 12,509	$ 141,966	$ 68,804	$ 54,460
Net income per share attributable to Class A and Class B common stockholders:
Basic		$ 0.24	$ 0.24	$ 0.27	$ 0.26	$ 0.16	$ 0.16	$ 0.10	$ 0.09	$ 1.01	$ 0.51	$ 0.41
Diluted		$ 0.22	$ 0.22	$ 0.25	$ 0.24	$ 0.15	$ 0.15	$ 0.09	$ 0.09	$ 0.92	$ 0.47	$ 0.38
Adoption of New Standard [Member]
Revenues:
Subscription services										$ 554,446	$ 434,316
Operating expenses:
Sales and marketing										130,898	116,803
Operating income										150,792	107,968
Net income										$ 141,966	$ 68,804
Net income per share attributable to Class A and Class B common stockholders:
Basic										$ 1.01	$ 0.51
Diluted										$ 0.92	$ 0.47
Adoption of New Standard [Member] | As Adjusted [Member]
Revenues:
Subscription services										$ 559,434	$ 440,815
Operating expenses:
Sales and marketing										128,749	110,582
Operating income										157,929	120,688
Net income										$ 151,176	$ 77,572
Net income per share attributable to Class A and Class B common stockholders:
Basic										$ 1.08	$ 0.57
Diluted										$ 0.98	$ 0.53

[1] Includes stock-based compensation as follows:   Cost of revenues: Cost of subscription services $1,448 $1,109 $563 Cost of professional services and other 8,476 6,002 3,858 Research and development 17,782 11,937 7,249 Sales and marketing 16,288 13,271 6,861 General and administrative 10,055 8,479 5,727 Total stock-based compensation $54,049 $40,798 $24,258