Summary of Business and Significant Accounting Policies - Schedule of Unaudited Condensed Consolidated Statement of Cash Flows (Detail) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Oct. 31, 2018	Oct. 31, 2017		Oct. 31, 2018	Oct. 31, 2017
Cash flows from operating activities
Net income		$ 64,085	$ 34,925	[1]	$ 158,681	$ 110,523	[1]
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred costs		4,595	4,203	[1]	13,697	12,338	[1]
Changes in operating assets and liabilities:
Accounts receivable		21,658	23,323	[1]	134,353	110,472	[1]
Unbilled accounts receivable		(5,212)	(4,852)	[1]	(6,641)	(5,331)	[1]
Deferred costs		(4,504)	(4,170)	[1]	(11,426)	(11,933)	[1]
Deferred revenue		(62,860)	(47,735)	[1]	(70,616)	(42,574)	[1]
Net cash provided by operating activities		41,556	32,234	[1]	278,954	232,001	[1]
Net cash (used in) provided by investing activities		(89,360)	(134,398)	[1]	(147,690)	(157,000)	[1]
Net change in cash, cash equivalents and restricted cash		(44,091)	(98,429)	[1]	147,462	93,392	[1]
Cash, cash equivalents, and restricted cash at beginning of period		512,940	410,428	[1]	321,387	218,607	[1]
Cash, cash equivalents, and restricted cash at end of period		$ 468,849	311,999	[1]	$ 468,849	311,999	[1]
As Reported [member] | Topic 606 [Member]
Cash flows from operating activities
Net income			34,393			108,260
Changes in operating assets and liabilities:
Accounts receivable			20,922			106,791
Deferred revenue			(49,328)			(40,301)
Net cash provided by operating activities			32,233			232,001
Change in restricted cash and deposits						(202)
Net cash (used in) provided by investing activities			(134,398)			(157,202)
Net change in cash, cash equivalents and restricted cash			(98,430)			93,190
Cash, cash equivalents, and restricted cash at beginning of period			409,226			217,606
Cash, cash equivalents, and restricted cash at end of period			310,796			310,796
Adjustments [Member] | Topic 606 [Member]
Cash flows from operating activities
Net income	[2]		532			2,263
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred costs	[2]		4,203			12,338
Changes in operating assets and liabilities:
Accounts receivable	[2]		2,401			3,681
Unbilled accounts receivable	[2]		(4,852)			(5,331)
Deferred costs	[2]		(4,170)			(11,933)
Deferred revenue	[2]		1,593			(2,273)
Net cash provided by operating activities	[2]		1
Change in restricted cash and deposits	[3]					202
Net cash (used in) provided by investing activities	[3]					202
Net change in cash, cash equivalents and restricted cash	[3]		1			202
Cash, cash equivalents, and restricted cash at beginning of period	[3]		1,202			1,001
Cash, cash equivalents, and restricted cash at end of period	[3]		$ 1,203			$ 1,203

[1] See note 1 of the notes to the condensed consolidated financial statements for a summary of adjustments.

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

[3] Adjusted to reflect the adoption of ASU 2016-18, “Statement of Cash Flows, Restricted Cash.”