Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	Jul. 31, 2019	Jan. 31, 2019
Property Plant And Equipment [Line Items]
Total property and equipment	$ 372,622	$ 329,526
Less: accumulated depreciation and amortization	(241,574)	(204,173)
Property and equipment, net	131,048	125,353
Test equipment
Property Plant And Equipment [Line Items]
Total property and equipment	191,846	170,930
Computer equipment and software
Property Plant And Equipment [Line Items]
Total property and equipment	135,178	117,330
Furniture and fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	7,732	6,980
Leasehold improvements
Property Plant And Equipment [Line Items]
Total property and equipment	$ 37,866	$ 34,286