Summary of Significant Accounting Policies - Revenue Recognition - ASC 606 (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
	Feb. 01, 2019	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018	Jan. 31, 2019
Assets:
Deferred contract acquisition costs, current		$ 34,017	$ 18,808	$ 34,017	$ 18,808	$ 28,847
Deferred contract acquisition costs, noncurrent		41,766	5,833	41,766	5,833	9,918
Liabilities
Accrued expenses		32,568		32,568		32,541
Deferred revenue, current		279,951		279,951		218,700
Deferred revenue, noncurrent		89,811		89,811		71,367
Stockholders' Equity:
Accumulated deficit		(573,574)		(573,574)		$ (519,126)
Condensed Consolidated Statement of Operations
Total revenue		108,108	55,701	204,185	102,990
Operating expenses
Sales and marketing		65,274	40,113	122,117	76,730
Net loss		$ (51,889)	$ (32,877)	$ (77,866)	$ (66,494)
Net loss per share, basic and diluted		$ (0.40)	$ (0.75)	$ (0.87)	$ (1.52)
Weighted average common shares outstanding, basic and diluted		130,091	44,105	89,335	43,864
ASC 2014-09
Revenue Recognition - ASC 606
Cumulative effect adjustment to opening accumulated deficit, net of tax	$ 23,400
Reduction in the amortization of deferred contract acquisition costs	23,700
Reduction in revenue	300
ASC 2014-09 | Impact of adoption
Assets:
Deferred contract acquisition costs, current	6,400	$ 381		$ 381
Deferred contract acquisition costs, noncurrent	$ 30,100	(33,523)		(33,523)
Liabilities
Accrued expenses		(555)		(555)
Deferred revenue, current		(168)		(168)
Stockholders' Equity:
Accumulated deficit		(32,419)		(32,419)
Condensed Consolidated Statement of Operations
Total revenue		(83)		(165)
Operating expenses
Sales and marketing		4,621		8,837
Net loss		(4,703)		(9,002)
ASC 2014-09 | Without adoption (ASC 605)
Assets:
Deferred contract acquisition costs, current		34,398		34,398
Deferred contract acquisition costs, noncurrent		8,243		8,243
Liabilities
Accrued expenses		32,013		32,013
Deferred revenue, current		279,783		279,783
Deferred revenue, noncurrent		89,811		89,811
Stockholders' Equity:
Accumulated deficit		(605,993)		(605,993)
Condensed Consolidated Statement of Operations
Total revenue		108,025		204,020
Operating expenses
Sales and marketing		69,895		130,954
Net loss		$ (56,592)		$ (86,868)
Net loss per share, basic and diluted		$ (0.44)		$ (0.97)