Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Income Statement [Abstract]
Revenue	$ 89,062	$ 100,490	$ 224,827	$ 222,789
Cost of revenue	32,448	34,167	82,445	76,289
Gross profit	56,614	66,323	142,382	146,500
Operating expenses:
Research and development	29,796	25,967	83,936	74,076
Selling, general and administrative	11,700	10,686	35,406	32,144
Total operating expenses	41,496	36,653	119,342	106,220
Income from operations	15,118	29,670	23,040	40,280
Other income, net	319	132	696	330
Income before income taxes	15,437	29,802	23,736	40,610
Provision for income taxes	3,713	757	6,145	1,150
Net income	$ 11,724	$ 29,045	$ 17,591	$ 39,460
Net income per share attributable to ordinary shareholders:
Basic	$ 0.35	$ 0.89	$ 0.53	$ 1.21
Diluted	$ 0.34	$ 0.84	$ 0.51	$ 1.15
Weighted-average shares used to compute net income per share attributable to ordinary shareholders:
Basic	33,128,761	32,670,784	33,203,432	32,552,077
Diluted	34,358,893	34,599,992	34,538,968	34,242,065