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Income Taxes - Actual Income Tax Expense Amounts (Detail) (USD $) | 12 Months Ended
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Jan. 31, 2014 | Jan. 31, 2013 | Jan. 31, 2012
Income Tax Disclosure [Abstract] |  |  |
Computed "expected" income tax | $ 24,267,000 | $ 12,510,000 | $ 4,068,000
Increase (decrease) resulting from: |  |  |
State income taxes, net | 2,574,000 | 1,459,000 | 460,000
Permanent differences | (1,105,000) | (730,000) | (138,000)
Federal income tax true-up and other adjustments | 255,000 | 401,000 | 166,000
Income tax expense | $ 25,991,000 | $ 13,640,000 | $ 4,556,000

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