Employee Benefits and Stock-based Compensation - Stock Option Activities (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding	1,853,390	2,281,909	3,358,706
Shares, Granted	110,500	179,700	428,781
Shares, Exercised	(235,923)	(567,888)	(1,456,944)
Shares, Forfeited	(16,708)	(40,331)	(48,634)
Shares, Expired	(7,735)
Shares, Outstanding	1,703,524	1,853,390	2,281,909
Shares, Exercisable	1,367,960
Weighted-Average Exercise Price, Outstanding	$ 19.36	$ 13.00	$ 6.92
Weighted-Average Exercise Price, Granted	47.82	71.36	36.33
Weighted-Average Exercise Price, Exercised	13.69	9.11	5.84
Weighted-Average Exercise Price, Forfeited	55.07	35.65	13.38
Weighted-Average Exercise Price, Expired	14.19
Weighted-Average Exercise Price, Outstanding	21.66	19.36	13.00
Weighted-Average Exercise Price, Exercisable	14.94
Weighted-Average Grant-date Fair Value, Granted	$ 18.76	$ 38.81	$ 21.37
Total Intrinsic Value of options Exercised	$ 10,788	$ 37,603	$ 46,427
Weighted-Average Remaining Contractual Term, Outstanding	5 years 1 month 28 days
Weighted-Average Remaining Contractual Term, Exercisable	4 years 5 months 1 day
Aggregate Intrinsic Value, Outstanding	$ 51,670
Aggregate Intrinsic Value, Exercisable	$ 49,016