Revenue - Financial Statement Impact of ASC 606 (Cash Flow) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jul. 31, 2018	Jul. 31, 2017		Jul. 31, 2018	Jul. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (38,085)	$ (39,285)		$ (74,722)	$ (79,371)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Amortization of deferred commissions	4,040	5,368		7,715	10,358
Changes in operating assets and liabilities:
Accounts receivable, net	(23,754)	(25,124)		47,936	12,222
Deferred commissions	(8,588)	(5,835)		(13,304)	(8,619)
Deferred revenue	14,568	16,524		(9,592)	(1,145)
Net cash provided by (used in) operating activities	(1,267)	$ (9,761)	[1]	17,173	$ (1,220)	[1]
Balances without adoption of ASC Topic 606 | Accounting Standards Update 2014-09
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	(40,970)			(79,101)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Amortization of deferred commissions	5,980			11,942
Changes in operating assets and liabilities:
Accounts receivable, net	(23,793)			47,511
Deferred commissions	(4,924)			(7,687)
Deferred revenue	11,888			(14,632)
Net cash provided by (used in) operating activities	(1,267)			17,173
Effect of Change | Accounting Standards Update 2014-09
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	2,885			4,379
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Amortization of deferred commissions	(1,940)			(4,227)
Changes in operating assets and liabilities:
Accounts receivable, net	39			425
Deferred commissions	(3,664)			(5,617)
Deferred revenue	$ 2,680			$ 5,040

[1] Adjusted due to the adoption of ASU 2016-18