Employee Benefits and Stock-based Compensation - Stock Option Activities (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding	2,281,909	3,358,706	4,344,535
Shares, Granted	179,700	428,781	255,520
Shares, Exercised	(567,888)	(1,456,944)	(1,160,286)
Shares, Forfeited	(40,331)	(48,634)	(81,063)
Shares, Outstanding	1,853,390	2,281,909	3,358,706
Shares, Exercisable	1,363,880
Shares, Vested and expected to vest	1,822,252
Weighted-Average Exercise Price, Outstanding	$ 13.00	$ 6.92	$ 6.07
Weighted-Average Exercise Price, Granted	71.36	36.33	18.14
Weighted-Average Exercise Price, Exercised	9.11	5.84	5.96
Weighted-Average Exercise Price, Forfeited	35.65	13.38	10.34
Weighted-Average Exercise Price, Outstanding	19.36	13.00	6.92
Weighted-Average Exercise Price, Exercisable	10.23
Weighted-Average Exercise Price, Vested and expected to vest	18.84
Weighted-Average Grant-date Fair Value, Granted	$ 38.81	$ 21.37	$ 10.85
Total Intrinsic Value of options Exercised	$ 37,603	$ 46,427	$ 18,217
Weighted-Average Remaining Contractual Term, Outstanding	5 years 10 months 21 days
Weighted-Average Remaining Contractual Term, Exercisable	4 years 11 months 5 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	5 years 10 months 2 days
Aggregate Intrinsic Value, Outstanding	$ 43,396
Aggregate Intrinsic Value, Exercisable	40,341
Aggregate Intrinsic Value, Vested and expected to vest	$ 43,285