Stock-Based Compensation - Summary of Activity under Company's Stock Option Plans (Detail) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
	Jul. 31, 2014	Jul. 31, 2014	Jan. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding, Beginning balance		916,150
Shares, Granted	0	180,500
Shares, Exercised		(153,800)
Shares, Outstanding, Ending balance	942,850	942,850	916,150
Shares, Exercisable	540,350	540,350	613,150
Weighted Average Exercise Price, Outstanding, Beginning balance		$ 17.36
Weighted Average Exercise Price, Granted		$ 27.09
Weighted Average Exercise Price, Exercised		$ 14.84
Weighted Average Exercise Price, Outstanding, Ending balance	$ 19.63	$ 19.63	$ 17.36
Weighted Average Exercise Price, Exercisable	$ 15.67	$ 15.67	$ 15.40
Weighted Average Remaining Contract Term, Granted		0 years
Weighted Average Remaining Contract Term, Exercised		0 years
Weighted Average Remaining Contract Term, Outstanding		6 years 7 months 24 days	6 years 15 days
Weighted Average Remaining Contract Term, Exercisable		5 years 11 months 1 day	5 years 1 month 2 days
Weighted Average Fair Value, Granted		$ 0
Weighted Average Fair Value, Exercised		$ 0
Weighted Average Fair Value, Outstanding, Beginning balance	$ 5.72	$ 5.72	$ 5.58
Weighted Average Fair Value, Exercisable	$ 5.91	$ 5.91	$ 6.15