Income Taxes - Reconciliation of the Federal Statutory Income Tax Rate and Effective Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018		Jan. 31, 2017
Income Tax Disclosure [Abstract]
Tax at federal statutory rate	$ (37,227)	$ (51,314)		$ (74,680)
State tax, net of federal benefit	(469)	351		276
Stock-based compensation expense	(28,437)	(9,953)		(5,242)
Research and development tax credits	(10,371)	(7,629)		(1,570)
Foreign rate differential	12,299	18,667		15,878
Change in valuation allowance	85,533	(44,784)		65,861
Foreign on-shoring intellectual property	(20,371)	0		0
Remeasurement of deferred tax assets and liabilities due to tax reform	0	97,280		0
Other	132	1,271		1,364
Provision for income taxes	$ 1,089	$ 3,889	[1]	$ 1,887	[1]

[1] *As adjusted to reflect the impact of the full retrospective adoption of ASC 606 - see Note 2.