Income Taxes - Reconciliation of the Federal Statutory Income Tax Rate and Effective Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Income Tax Disclosure [Abstract]
Tax at federal statutory rate	$ (57,144)	$ (82,682)	$ (72,142)
State tax, net of federal benefit	351	276	152
Stock-based compensation expense	(9,953)	(5,242)	10,866
Research and development tax credits	(7,629)	(1,570)	(3,832)
Foreign rate differential	18,667	15,878	7,106
Change in valuation allowance	(48,703)	73,863	58,979
Remeasurement of deferred tax assets and liabilities	107,029	0	0
Other	1,271	1,364	440
Provision for income taxes	$ 3,889	$ 1,887	$ 1,569