Employee Benefits and Stock-Based Compensation - Stock Option Activities (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Apr. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding	4,344,535
Shares, Granted	60,000
Shares, Exercised	(158,871)
Shares, Forfeited	(31,561)
Shares, Outstanding	4,214,103
Shares, Exercisable	3,084,125
Shares, Vested and expected to vest	4,140,490
Weighted-Average Exercise Price, Outstanding	$ 6.07
Weighted-Average Exercise Price, Granted	$ 13.74
Weighted-Average Exercise Price, Exercised	$ 3.11
Weighted-Average Exercise Price, Forfeited	$ 8.45
Weighted-Average Exercise Price, Outstanding	$ 6.27
Weighted-Average Exercise Price, Exercisable	$ 5.42
Weighted-Average Exercise Price, Vested and expected to vest	$ 6.23
Weighted-Average Grant-date Fair Value, Granted	$ 8.15
Total Intrinsic Value of options Exercised, Exercised	$ 1,689
Weighted-Average Remaining Contractual Term, Outstanding	6 years 8 months 1 day
Weighted-Average Remaining Contractual Term, Exercisable	6 years 26 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	6 years 7 months 21 days
Aggregate Intrinsic Value, Outstanding	31,311
Aggregate Intrinsic Value, Exercisable	25,522
Aggregate Intrinsic Value, Vested and expected to vest	$ 30,940