Basis of Presentation and Summary of Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Statement of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jul. 31, 2018	Jul. 31, 2017		Jul. 31, 2018	Jul. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	$ (60,123)	$ (58,411)	[1],[2]	$ (124,427)	$ (115,570)	[3]
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Deferred commissions				(4,155)	(9,587)	[3]
Accrued compensation and other liabilities				(7,458)	(2,993)	[3]
Deferred revenue				39,144	24,251	[3]
Cash used in operating activities				27,080	(14,492)	[3]
Cash, cash equivalents and restricted cash, beginning of period				258,820	196,409	[3]
Cash, cash equivalents and restricted cash, end of period	$ 386,235	184,628	[3]	$ 386,235	184,628	[3]
As Previously Reported
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss		(61,701)			(124,075)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Deferred commissions					(4,607)
Accrued compensation and other liabilities					310
Deferred revenue					24,473
Cash used in operating activities					(14,492)
Cash, cash equivalents and restricted cash, beginning of period					183,675
Cash, cash equivalents and restricted cash, end of period		171,894			171,894
Adjustment | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss		3,290			8,505
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Deferred commissions					(4,980)
Accrued compensation and other liabilities					(3,303)
Deferred revenue					(222)
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			$ 12,734

[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 ASU 2016-18, which we adopted on February 1, 2018