Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018		Jan. 31, 2017
Property Plant And Equipment [Line Items]
Total property and equipment	$ 329,526	$ 235,035
Less: accumulated depreciation and amortization	(204,173)	(145,893)
Property and equipment, net	125,353	89,142	[1]
Depreciation and amortization	68,300	60,200		$ 48,800
Test equipment
Property Plant And Equipment [Line Items]
Total property and equipment	170,930	142,311
Computer equipment and software
Property Plant And Equipment [Line Items]
Total property and equipment	117,330	72,329
Furniture and fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	6,980	5,363
Leasehold improvements
Property Plant And Equipment [Line Items]
Total property and equipment	$ 34,286	$ 15,032

[1] * As adjusted to reflect the impact of the full retrospective adoption of ASC 606