Note F - Debt Facilities (Details Textual) - USD ($)							6 Months Ended
	Dec. 12, 2016	Oct. 31, 2016	Dec. 15, 2015	Oct. 08, 2014	Jun. 24, 2013	Feb. 04, 2013	Oct. 31, 2016	Oct. 31, 2015	Apr. 30, 2016	Feb. 18, 2016	Feb. 17, 2016	Feb. 13, 2014	Sep. 30, 2012	Mar. 09, 2012
Revolving Credit Facility [Member] | Minimum [Member] | Subsequent Event [Member]
Debt Agreement, Accounts Receivable Advances, Term Range One	3 years 30 days
Debt Agreement, Accounts Receivable Advances, Term Range Two	3 years 210 days
Revolving Credit Facility [Member] | Minimum [Member]
Contract Term of Contracts Included by Credit Facilities Amendment						3 years
Revolving Credit Facility [Member] | Maximum [Member] | Subsequent Event [Member]
Debt Agreement, Accounts Receivable Advances, Term Range One	3 years 180 days
Debt Agreement, Accounts Receivable Advances, Term Range Two	5 years
Revolving Credit Facility [Member] | Maximum [Member]
Contract Term of Contracts Included by Credit Facilities Amendment						3 years 180 days
Revolving Credit Facility [Member] | Credit Facilities, Amendment Number 3 [Member]
Line of Credit Facility, Additional Borrowing Capacity, Accordion Feature					$ 55,000,000
Line of Credit Facility, Decrease in Pricing Tiers, Percent					0.25%
Revolving Credit Facility [Member] | Credit Facilities, Amendment Number 4 [Member]
Maximum Allowable Capital Expenditures By Credit Facilities Amendment												$ 10,000,000
Revolving Credit Facility [Member] | Credit Facilities Amendment Number 5 [Member]
Line of Credit Facility Increase in Pricing Tiers Percent				0.125%
Dividend Restrictions Maximum Aggregate Amount of Stock Repurchases				$ 40,000,000
Dividend Restrictions Percentage of Sum of Borrowing Bases				30.00%
Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate							2.375%
Revolving Credit Facility [Member] | Subsequent Event [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 200,000,000
Dividend Restrictions Maximum Aggregate Amount of Stock Repurchases	40,000,000
Line of Credit Facility, Additional Borrowing Capacity, Accordion Feature	$ 50,000,000
Debt Agreement, Accounts Receivable Advances, Term Range One, Rate	55.00%
Debt Agreement, Accounts Receivable Advances, Term Range Two, Rate	50.00%
Revolving Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity		$ 172,500					$ 172,500			$ 172,500,000	$ 145,000,000		$ 145,000,000	$ 125,000,000
Dividend Restrictions Maximum Aggregate Amount of Stock Repurchases							40,000,000
Line of Credit Facility, Total Increase in Borrowing Capacity										27,500,000
Line of Credit Facility, Additional Borrowing Capacity, Accordion Feature		$ 45,000,000					$ 45,000,000			55,000,000
Line of Credit Facility, Maximum Borrowing Capacity, Accordion Feature										$ 200,000,000
Line of Credit Facility, Distribution Limitations Percentage of Sum of Borrowing Bases							30.00%
Line of Credit Facility, Distribution Limitations Percentage of Consolidated Net Income							75.00%
Line of Credit Facility Distribution Limitations Minimum Percentage of Aggregate Funds Available							12.50%
Debt Agreement, Accounts Receivable Advances, Term Range One, Rate		50.00%
Debt Agreement, Accounts Receivable Advances, Term Range Two, Rate		45.00%
Note Payable Related to the Property Purchase Agreement [Member]
Debt Instrument, Face Amount			$ 550,000
Debt Instrument, Periodic Payment			$ 10,005
Debt Instrument, Interest Rate, Stated Percentage			3.50%
Long-term Debt		$ 465,000					$ 465,000		$ 516,000
Line of Credit Facility, Distribution Limitations Percentage of Sum of Borrowing Bases							30.00%
Line of Credit Facility, Distribution Limitations Percentage of Consolidated Net Income							75.00%
Line of Credit Facility Distribution Limitations Minimum Percentage of Aggregate Funds Available							12.50%
Amortization of Debt Issuance Costs and Discounts							$ 140,000	$ 96,000
Debt Issuance Costs, Gross		$ 256,000					$ 256,000		$ 396,000