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			6 Months Ended
	Jul. 31, 2018	Jul. 31, 2017		Jul. 31, 2018	Jul. 31, 2017
Revenue:
Product	$ 241,137	$ 179,669	[1]	$ 436,586	$ 322,519
Support subscription	67,747	45,001	[1]	128,243	84,796
Total revenue	308,884	224,670	[1]	564,829	407,315
Gross profit	206,165	148,219	[1]	372,480	267,316
Sales and marketing	143,749	117,552	[1]	266,116	209,315
Total operating expenses	261,371	209,075	[1]	489,560	386,362
Loss from operations	(55,206)	(60,856)	[1]	(117,080)	(119,046)
Loss before provision for income taxes	(59,238)	(57,590)	[1]	(122,111)	(113,785)
Net loss	$ (60,123)	$ (58,411)	[1],[2]	$ (124,427)	$ (115,570)	[3]
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.26)	$ (0.28)	[1]	$ (0.55)	$ (0.56)
As Previously Reported
Revenue:
Product		$ 175,013			$ 313,438
Support subscription		49,448			93,654
Total revenue		224,461			407,092
Gross profit		148,010			267,093
Sales and marketing		120,633			217,597
Total operating expenses		212,156			394,644
Loss from operations		(64,146)			(127,551)
Loss before provision for income taxes		(60,880)			(122,290)
Net loss		$ (61,701)			$ (124,075)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)		$ (0.29)			$ (0.60)
Adjustment | Accounting Standards Update 2014-09
Revenue:
Product		$ 4,656			$ 9,081
Support subscription		(4,447)			(8,858)
Total revenue		209			223
Gross profit		209			223
Sales and marketing		(3,081)			(8,282)
Total operating expenses		(3,081)			(8,282)
Loss from operations		3,290			8,505
Loss before provision for income taxes		3,290			8,505
Net loss		$ 3,290			$ 8,505
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)		$ 0.01			$ 0.04

[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 ASU 2016-18, which we adopted on February 1, 2018