Basis of Presentation and Summary of Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Statement of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 30, 2018	Apr. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	$ (64,304)	$ (57,159)	[1],[2],[3]
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Deferred commissions	1,269	(1,367)	[1]
Accrued compensation and other liabilities	(29,881)	(24,194)	[1]
Deferred revenue	14,510	8,384	[1]
Cash used in operating activities	18,596	(14,301)	[1]
Cash, cash equivalents and restricted cash, beginning of period	258,820	196,409	[1]
Cash, cash equivalents and restricted cash, end of period	$ 751,639	181,491	[1]
As Previously Reported
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss		(62,374)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Deferred commissions		(362)
Accrued compensation and other liabilities		(19,998)
Deferred revenue		8,398
Cash used in operating activities		(14,301)
Cash, cash equivalents and restricted cash, beginning of period		183,675
Cash, cash equivalents and restricted cash, end of period		168,757
Adjustment | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss		5,215
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Deferred commissions		(1,005)
Accrued compensation and other liabilities		(4,196)
Deferred revenue		(14)
Cash used in operating activities		0
Adjustment | Accounting Standards Update 2016-18
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Cash, cash equivalents and restricted cash, beginning of period		12,734
Cash, cash equivalents and restricted cash, end of period		$ 12,734

[1] * 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

[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, which we adopted on February 1, 2018.