Basis of Presentation and Summary of Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Statement of Operations) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			9 Months Ended
	Oct. 31, 2018	Oct. 31, 2017		Oct. 31, 2018	Oct. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue	$ 372,779	$ 277,591	[1]	$ 937,608	$ 684,906	[1]
Gross profit	249,120	181,732	[1]	621,600	449,048	[1]
Sales and marketing	146,903	116,971	[1]	413,019	326,286	[1]
Total operating expenses	276,337	211,304	[1]	765,897	597,666	[1]
Loss from operations	(27,217)	(29,572)	[1]	(144,297)	(148,618)	[1]
Loss before provision for income taxes	(30,106)	(28,434)	[1]	(152,217)	(142,219)	[1]
Net loss	$ (28,180)	$ (29,404)	[1],[2]	$ (152,607)	$ (144,974)	[1],[2],[3]
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.12)	$ (0.14)	[1]	$ (0.66)	$ (0.69)	[1]
Product
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue	$ 298,863	$ 227,772	[1]	$ 735,449	$ 550,291	[1]
Support subscription
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue	$ 73,916	49,819	[1]	$ 202,159	134,615	[1]
Adjustment | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue		(83)			140
Gross profit		(83)			140
Sales and marketing		(12,328)			(20,610)
Total operating expenses		(12,328)			(20,610)
Loss from operations		12,245			20,750
Loss before provision for income taxes		12,245			20,750
Net loss		$ 12,245			$ 20,750
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)		$ 0.06			$ 0.10
Adjustment | Product | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue		$ 4,576			$ 13,657
Adjustment | Support subscription | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue		(4,659)			(13,517)
As Previously Reported
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue		277,674			684,766
Gross profit		181,815			448,908
Sales and marketing		129,299			346,896
Total operating expenses		223,632			618,276
Loss from operations		(41,817)			(169,368)
Loss before provision for income taxes		(40,679)			(162,969)
Net loss		$ (41,649)			$ (165,724)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)		$ (0.20)			$ (0.79)
As Previously Reported | Product
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue		$ 223,196			$ 536,634
As Previously Reported | Support subscription
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenue		$ 54,478			$ 148,132

[1] * Prior period information has been adjusted to reflect the adoption impact of ASC 606, which we adopted on February 1, 2018.

[2] * Prior period information has been adjusted to reflect the adoption impact of ASC 606, which we adopted on February 1, 2018.

[3] * Prior period information has been adjusted to reflect the adoption impact of ASC 606 and Accounting Standards Update No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (ASU 2016-18), which we adopted on February 1, 2018