Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Income Statement [Abstract]
Revenue	$ 57,286	$ 89,062	$ 176,698	$ 224,827
Cost of revenue	22,701	32,448	69,208	82,445
Gross profit	34,585	56,614	107,490	142,382
Operating expenses:
Research and development	31,653	29,796	95,446	83,936
Selling, general and administrative	12,354	11,700	38,098	35,406
Total operating expenses	44,007	41,496	133,544	119,342
Income (loss) from operations	(9,422)	15,118	(26,054)	23,040
Other income, net	993	319	2,517	696
Income (loss) before income taxes	(8,429)	15,437	(23,537)	23,736
Provision for income taxes	592	3,713	2,367	6,145
Net income (loss)	$ (9,021)	$ 11,724	$ (25,904)	$ 17,591
Net income (loss) per share attributable to ordinary shareholders:
Basic	$ (0.28)	$ 0.35	$ (0.79)	$ 0.53
Diluted	$ (0.28)	$ 0.34	$ (0.79)	$ 0.51
Weighted-average shares used to compute net income (loss) per share attributable to ordinary shareholders:
Basic	32,171,890	33,128,761	32,908,614	33,203,432
Diluted	32,171,890	34,358,893	32,908,614	34,538,968