Revenue - Financial Statement Impact of ASC 606 (Income Statement) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Apr. 30, 2018	Apr. 30, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue	$ 140,507	$ 117,222
Operating expenses:
Sales and marketing	76,998	70,663
Loss from operations	(35,860)	(39,979)
Net loss	$ (36,637)	$ (40,086)
Net loss per common share, basic and diluted	$ (0.26)	$ (0.30)
Weighted-average shares used to compute net loss per share, basic and diluted	138,524	131,469
Balances without adoption of ASC Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue	$ 143,253
Operating expenses:
Sales and marketing	81,238
Loss from operations	(37,354)
Net loss	$ (38,131)
Net loss per common share, basic and diluted	$ (0.28)
Weighted-average shares used to compute net loss per share, basic and diluted	138,524
Effect of Change Higher/(Lower) | Accounting Standards Update 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Revenue	$ (2,746)
Operating expenses:
Sales and marketing	(4,240)
Loss from operations	1,494
Net loss	$ 1,494
Net loss per common share, basic and diluted	$ 0.01
Weighted-average shares used to compute net loss per share, basic and diluted	138,524