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Stock-Based Compensation - Summary of Activity under Option and Stock Plans (Detail) (USD $) | 12 Months Ended
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Jan. 31, 2014 | Jan. 31, 2013 | Jan. 31, 2012 | Jan. 31, 2011
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |  |  |  |
Shares, Outstanding, Beginning balance | 926,224 | 817,186 | 675,724 |
Weighted Average Exercise Price, Outstanding, Beginning balance | $ 14.34 | $ 12.10 | $ 11.29 |
Shares, Granted | 303,000 | 293,000 | 212,500 |
Shares, Exercised | (309,074) | (153,962) | (55,038) |
Shares, Forfeited | (4,000) | (30,000) | (16,000) |
Shares, Outstanding, Ending balance | 916,150 | 926,224 | 817,186 | 675,724
Shares, Exercisable | 613,150 |  |  |
Weighted Average Exercise Price, Granted | $ 21.32 | $ 17.36 | $ 13.92 |
Weighted Average Exercise Price, Exercised | $ 12.20 | $ 9.33 | $ 9.36 |
Weighted Average Exercise Price, Forfeited | $ 17.33 | $ 8.66 | $ 11.36 |
Weighted Average Exercise Price, Outstanding, Ending balance | $ 17.36 | $ 14.34 | $ 12.10 | $ 11.29
Weighted Average Exercise Price, Exercisable | $ 15.40 |  |  |
Weighted Average Remaining Term, Outstanding | 6 years 15 days | 5 years 4 months 21 days | 4 years 11 months 9 days | 5 years 9 months 11 days
Weighted Average Remaining Term, Exercisable | 5 years 1 month 2 days |  |  |
Weighted Average Fair Value, Outstanding, Beginning balance | $ 5.58 | $ 5.93 | $ 5.68 | $ 5.79
Weighted Average Fair Value, Exercisable | $ 6.15 |  |  |

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