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, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Numerator:
Net income	$ 11,724	$ 29,045	$ 17,591	$ 39,460
Denominator:
Weighted-average ordinary shares - basic	33,128,761	32,670,784	33,203,432	32,552,077
Effect of potentially dilutive securities:
Employee stock options	913,496	1,159,739	967,903	1,094,786
Restricted stock and restricted stock units	311,430	753,178	363,476	583,144
Employee stock purchase plan	5,206	16,291	4,157	12,058
Weighted-average ordinary shares - diluted	34,358,893	34,599,992	34,538,968	34,242,065
Net income per ordinary share:
Basic	$ 0.35	$ 0.89	$ 0.53	$ 1.21
Diluted	$ 0.34	$ 0.84	$ 0.51	$ 1.15