Net Income Per Ordinary Share - Computation of Basic and Diluted Net Income Per Ordinary Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 31, 2015	Oct. 31, 2014	Oct. 31, 2015	Oct. 31, 2014
Numerator:
Net income	$ 29,461	$ 18,327	$ 71,412	$ 32,897
Less: amount allocable to unvested early exercised options	0	(1)	0	(8)
Net income allocable to ordinary shareholders - basic	29,461	18,326	71,412	32,889
Undistributed earnings reallocated to ordinary shareholders	0	0	0	1
Net income allocable to ordinary shareholders - diluted	$ 29,461	$ 18,326	$ 71,412	$ 32,890
Denominator:
Weighted-average ordinary shares outstanding	31,815,588	30,009,218	31,476,724	29,474,364
Less: weighted-average unvested early exercised options subject to repurchase	0	(2,322)	(56)	(7,186)
Weighted-average ordinary shares - basic	31,815,588	30,006,896	31,476,668	29,467,178
Effect of potentially dilutive securities:
Employee stock options	1,199,065	1,719,140	1,316,228	1,902,988
Restricted stock	881,605	646,661	957,263	633,799
Employee stock purchase plan	2,944	9,829	8,382	10,408
Weighted-average ordinary shares - diluted	33,899,202	32,382,526	33,758,541	32,014,373
Net income per ordinary share:
Basic	$ 0.93	$ 0.61	$ 2.27	$ 1.12
Diluted	$ 0.87	$ 0.57	$ 2.12	$ 1.03