Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Income Statement [Abstract]
Revenue	$ 227,768	$ 295,402	$ 310,297
Cost of revenue	89,624	107,669	105,283
Gross profit	138,144	187,733	205,014
Operating expenses:
Research and development	128,084	115,510	101,205
Selling, general and administrative	50,480	47,792	43,446
Total operating expenses	178,564	163,302	144,651
Income (loss) from operations	(40,420)	24,431	60,363
Other income, net	5,868	1,298	518
Income (loss) before income taxes	(34,552)	25,729	60,881
Provision (benefit) for income taxes	(4,105)	6,877	3,071
Net income (loss)	$ (30,447)	$ 18,852	$ 57,810
Net income (loss) per share attributable to ordinary shareholders:
Basic	$ (0.93)	$ 0.57	$ 1.77
Diluted	$ (0.93)	$ 0.55	$ 1.68
Weighted-average shares used to compute net income (loss) per share attributable to ordinary shareholders:
Basic	32,713,606	33,224,803	32,671,221
Diluted	32,713,606	34,583,150	34,327,724