Basis of Presentation and Summary of Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Balance Sheet) (Details) - USD ($) $ in Thousands	Oct. 31, 2018	Jul. 31, 2018	Jan. 31, 2018
Assets:
Deferred commissions, current	$ 24,100		$ 21,088	[1]
Deferred commissions, non-current	72,340		66,225	[1]
Total deferred commissions	96,440	$ 91,469	87,313
Liabilities:
Deferred revenue, current	232,570		191,229	[1]
Deferred revenue, non-current	228,618		182,873	[1]
Total deferred revenue	461,188	$ 413,247	374,102
Stockholders' equity:
Accumulated deficit	$ (1,056,194)		(903,587)	[1]
As Previously Reported
Assets:
Deferred commissions, current			22,437
Deferred commissions, non-current			20,288
Total deferred commissions			42,725
Liabilities:
Deferred revenue, current			209,377
Deferred revenue, non-current			196,632
Total deferred revenue			406,009
Stockholders' equity:
Accumulated deficit			(980,082)
Adjustment | Accounting Standards Update 2014-09
Assets:
Deferred commissions, current			(1,349)
Deferred commissions, non-current			45,937
Total deferred commissions			44,588
Liabilities:
Deferred revenue, current			(18,148)
Deferred revenue, non-current			(13,759)
Total deferred revenue			(31,907)
Stockholders' equity:
Accumulated deficit			$ 76,495

[1] *Prior period information has been adjusted to reflect the adoption impact of Accounting Standards Codification 606, Revenue from Contracts with Customers (ASC 606), which we adopted on February 1, 2018.