Basis of Presentation and Summary of Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Statement of Cash Flows) (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Oct. 31, 2018	Oct. 31, 2017		Oct. 31, 2018	Oct. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss		$ (28,180)	$ (29,404)	[1],[2]	$ (152,607)	$ (144,974)	[1],[2],[3]
Adjustments to reconcile net loss to net cash provided by operating activities:
Deferred commissions					(9,127)	(13,969)	[3]
Accrued compensation and other liabilities					7,592	359	[3]
Deferred revenue					87,005	54,264	[3]
Cash provided by operating activities					83,629	13,756	[3]
Net increase in restricted cash	[3]					0
Net cash used in investing activities					(468,103)	(51,261)	[3]
Net increase (decrease) in cash, cash equivalents and restricted cash					163,643	393	[3]
Cash, cash equivalents and restricted cash, beginning of period					258,820	196,409	[3]
Cash, cash equivalents and restricted cash, end of period		$ 422,463	196,802	[3]	$ 422,463	196,802	[3]
As Previously Reported
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss			(41,649)			(165,724)
Adjustments to reconcile net loss to net cash provided by operating activities:
Deferred commissions						(7,629)
Accrued compensation and other liabilities						14,629
Deferred revenue						54,404
Cash provided by operating activities						13,756
Net increase in restricted cash						(2,029)
Net cash used in investing activities						(53,290)
Net increase (decrease) in cash, cash equivalents and restricted cash						(1,636)
Cash, cash equivalents and restricted cash, beginning of period						183,675
Cash, cash equivalents and restricted cash, end of period			182,039			182,039
Adjustment | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss			12,245			20,750
Adjustments to reconcile net loss to net cash provided by operating activities:
Deferred commissions						(6,340)
Accrued compensation and other liabilities						(14,270)
Deferred revenue						(140)
Cash provided by operating activities						0
Adjustment | Accounting Standards Update 2016-18
Adjustments to reconcile net loss to net cash provided by operating activities:
Net increase in restricted cash						2,029
Net cash used in investing activities						2,029
Net increase (decrease) in cash, cash equivalents and restricted cash						2,029
Cash, cash equivalents and restricted cash, beginning of period						12,734
Cash, cash equivalents and restricted cash, end of period			$ 14,763			$ 14,763

[1] * Prior period information has been adjusted to reflect the adoption impact of ASC 606, 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 and Accounting Standards Update No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (ASU 2016-18), which we adopted on February 1, 2018