Stock-Based Compensation - Summary of Activity under Company's Stock Option Plans (Detail) (USD $)	3 Months Ended		12 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Jan. 31, 2015	Jan. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares, Outstanding, Beginning balance	876,350	916,150	916,150
Shares, Granted	100,000	180,500
Shares, Exercised	(37,750)	(83,500)
Shares, Forfeited	(6,000)
Shares, Outstanding, Ending balance	932,600	1,013,150	876,350	916,150
Shares, Exercisable	707,600	600,650
Weighted Average Exercise Price, Outstanding, Beginning balance	$ 22.34	$ 17.36	$ 17.36
Weighted Average Exercise Price, Granted	$ 32.68	$ 27.09
Weighted Average Exercise Price, Exercised	$ 11.48	$ 13.50
Weighted Average Exercise Price, Forfeited	$ 17.33
Weighted Average Exercise Price, Outstanding, Ending balance	$ 23.92	$ 19.41	$ 22.34	$ 17.36
Weighted Average Exercise Price, Exercisable	$ 21.01	$ 15.75
Weighted Average Remaining Term, Outstanding	7 years 3 months 26 days	6 years 9 months 4 days	7 years 29 days	6 years 15 days
Weighted Average Remaining Term, Exercisable	6 years 9 months 26 days	5 years 11 months 23 days
Weighted Average Fair Value, Outstanding	$ 6.38	$ 5.65	$ 6.01	$ 5.58
Weighted Average Fair Value, Exercisable	$ 5.72	$ 5.81