Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017
Income Statement [Abstract]
Revenue	$ 62,474	$ 71,630	$ 119,412	$ 135,765
Cost of revenue	24,461	26,825	46,507	49,997
Gross profit	38,013	44,805	72,905	85,768
Operating expenses:
Research and development	32,129	27,538	63,793	54,140
Selling, general and administrative	12,566	11,962	25,744	23,706
Total operating expenses	44,695	39,500	89,537	77,846
Income (loss) from operations	(6,682)	5,305	(16,632)	7,922
Other income, net	732	224	1,524	377
Income (loss) before income taxes	(5,950)	5,529	(15,108)	8,299
Provision for income taxes	927	2,226	1,775	2,432
Net income (loss)	$ (6,877)	$ 3,303	$ (16,883)	$ 5,867
Net income (loss) per share attributable to ordinary shareholders:
Basic	$ (0.21)	$ 0.10	$ (0.51)	$ 0.18
Diluted	$ (0.21)	$ 0.10	$ (0.51)	$ 0.17
Weighted-average shares used to compute net income (loss) per share attributable to ordinary shareholders:
Basic	33,219,152	33,227,717	33,276,976	33,240,767
Diluted	33,219,152	34,572,927	33,276,976	34,629,004