Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 235,035	$ 175,302
Less: accumulated depreciation and amortization	(145,893)	(93,607)
Property and equipment, net	89,142	81,695
Depreciation and amortization	60,200	48,800	$ 31,000
Test equipment
Property Plant And Equipment [Line Items]
Total property and equipment, gross	142,311	105,955
Computer equipment and software
Property Plant And Equipment [Line Items]
Total property and equipment, gross	72,329	54,521
Furniture and fixtures
Property Plant And Equipment [Line Items]
Total property and equipment, gross	5,363	4,494
Leasehold improvements
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 15,032	$ 10,332