Revenue - Financial Statement Impact of ASC 606 (Cash Flow) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Oct. 31, 2018	Oct. 31, 2017		Oct. 31, 2018	Oct. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (40,196)	$ (42,924)		$ (114,918)	$ (122,295)
Adjustments to reconcile net loss to net cash provided by operating activities:
Amortization of deferred commissions	4,516	5,393		12,231	15,751
Changes in operating assets and liabilities:
Accounts receivable, net	9,065	12,023		57,001	24,245
Deferred commissions	(9,753)	(4,616)		(23,057)	(13,235)
Deferred revenue	(276)	12,167		(9,868)	11,022
Net cash provided by operating activities	6,816	$ 14,094	[1]	23,989	$ 12,874	[1]
Balances without adoption of ASC Topic 606 | Accounting Standards Update 2014-09
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	(43,017)			(122,118)
Adjustments to reconcile net loss to net cash provided by operating activities:
Amortization of deferred commissions	6,177			18,119
Changes in operating assets and liabilities:
Accounts receivable, net	9,124			56,635
Deferred commissions	(6,083)			(13,770)
Deferred revenue	(2,845)			(17,477)
Net cash provided by operating activities	6,816			23,989
Effect of Change | Accounting Standards Update 2014-09
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	2,821			7,200
Adjustments to reconcile net loss to net cash provided by operating activities:
Amortization of deferred commissions	(1,661)			(5,888)
Changes in operating assets and liabilities:
Accounts receivable, net	(59)			366
Deferred commissions	(3,670)			(9,287)
Deferred revenue	$ 2,569			$ 7,609

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