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Significant Accounting Policies (Details) $ in Thousands | 12 Months Ended
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Apr. 30, 2018 USD ($) people state segment store merchandise_category | Apr. 30, 2017 USD ($) | Apr. 30, 2016 USD ($)
Accounting Policies [Abstract] |  |  |
Number of stores | store | 2,073 |  |
Number of states in which entity operates | state | 16 |  |
Population of communities (many less than) | people | 5,000 |  |
Concentration Risk |  |  |
Excess of current cost over the stated LIFO Value | $ 73,494 | $ 65,593 |
Goodwill | 140,258 | 132,806 |
Asset impairment charges | 507 | 705 | $ 1,625
Recorded asset retirement obligation (net of amortization) | 11,280 | 10,421 |
Discounted liability of asset retirement obligation | 17,087 | 15,899 |
Self insurance reserve | $ 39,777 | 37,984 |
Number of operating segments | segment | 1 |  |
Number of reportable segments | segment | 1 |  |
Number of merchandise categories | merchandise_category | 3 |  |
Insurance accruals, current | $ 20,029 | 18,816 |
Insurance accruals, net of current portion | 19,748 | 19,168 |
Fuel |  |  |
Concentration Risk |  |  |
Excise taxes collected | $ 919,000 | $ 866,000 | $ 818,000
Fuel | Retail Sales |  |  |
Concentration Risk |  |  |
Concentration risk percentage | 61.00% |  |
Grocery & other merchandise | Retail Sales |  |  |
Concentration Risk |  |  |
Concentration risk percentage | 27.00% |  |
Prepared food & fountain | Retail Sales |  |  |
Concentration Risk |  |  |
Concentration risk percentage | 12.00% |  |

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