Revenue - Financial Statement Impact of ASC 606 (Income Statement) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue	$ 155,944	$ 129,304	$ 444,673	$ 369,467
Operating expenses:
Sales and marketing	84,490	81,670	238,472	225,604
Loss from operations	(39,464)	(42,559)	(112,543)	(121,534)
Net loss	$ (40,196)	$ (42,924)	$ (114,918)	$ (122,295)
Net loss per common share, basic and diluted	$ (0.28)	$ (0.32)	$ (0.82)	$ (0.92)
Weighted-average shares used to compute net loss per share, basic and diluted	142,366	134,636	140,559	133,044
Balances without adoption of ASC Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue	$ 158,454		$ 452,648
Operating expenses:
Sales and marketing	89,821		253,647
Loss from operations	(42,285)		(119,743)
Net loss	$ (43,017)		$ (122,118)
Net loss per common share, basic and diluted	$ (0.30)		$ (0.87)
Weighted-average shares used to compute net loss per share, basic and diluted	142,366		140,559
Effect of Change | Accounting Standards Update 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue	$ (2,510)		$ (7,975)
Operating expenses:
Sales and marketing	(5,331)		(15,175)
Loss from operations	2,821		7,200
Net loss	$ 2,821		$ 7,200
Net loss per common share, basic and diluted	$ 0.02		$ 0.05
Weighted-average shares used to compute net loss per share, basic and diluted	142,366		140,559