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			6 Months Ended
		Jul. 31, 2018	Jul. 31, 2017		Jul. 31, 2018	Jul. 31, 2017
Revenues:
Subscription services		$ 209,609	$ 167,795	[1]	$ 405,156	$ 327,567	[1]
Operating expenses:
Sales and marketing	[2]	38,222	32,070	[1]	72,607	62,211	[1]
Operating income		52,818	38,067	[1]	96,774	76,930	[1]
Provision for income taxes		5,874	2,323	[1]	7,659	4,781	[1]
Net income		$ 50,286	$ 38,602	[1]	$ 94,596	$ 75,598	[1]
Net income per share attributable to Class A and Class B common stockholders:
Basic		$ 0.35	$ 0.28	[1]	$ 0.66	$ 0.54	[1]
Diluted		$ 0.32	$ 0.25	[1]	$ 0.61	$ 0.49	[1]
Subscription services [Member]
Revenues:
Subscription services		$ 169,592	$ 135,550	[1]	$ 325,595	$ 264,681	[1]
As Reported [member] | Topic 606 [Member]
Operating expenses:
Sales and marketing			32,017			61,827
Operating income			36,898			74,237
Provision for income taxes			1,912			3,819
Net income			$ 37,844			$ 73,867
Net income per share attributable to Class A and Class B common stockholders:
Basic			$ 0.27			$ 0.53
Diluted			$ 0.25			$ 0.48
As Reported [member] | Subscription services [Member] | Topic 606 [Member]
Revenues:
Subscription services			$ 134,340			$ 261,617
Adjustments [Member] | Topic 606 [Member]
Operating expenses:
Sales and marketing	[3]		53			384
Operating income	[3]		1,169			2,693
Provision for income taxes	[3]		411			962
Net income	[3]		$ 758			$ 1,731
Net income per share attributable to Class A and Class B common stockholders:
Basic	[3]		$ 0.01			$ 0.01
Diluted	[3]					$ 0.01
Adjustments [Member] | Subscription services [Member] | Topic 606 [Member]
Revenues:
Subscription services	[3]		$ 1,210			$ 3,064

[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 $416 $376 $761 $718 Cost of professional services and other 2,657 2,133 4,985 3,822 Research and development 5,795 4,349 10,462 8,151 Sales and marketing 4,830 4,173 8,918 8,020 General and administrative 6,020 2,349 11,603 4,457 Total stock-based compensation $19,718 $13,380 $36,729 $25,168

[3] Adjusted to reflect the adoption of ASU 2014-09, “Revenue from Contracts with Customers (Topic 606).”