Note F - Debt Facilities (Details) (USD $)	6 Months Ended			0 Months Ended		1 Months Ended	0 Months Ended		6 Months Ended
	Oct. 31, 2014	Oct. 31, 2013	Sep. 30, 2012 Credit Facilities, Amendment No. 1 [Member] Revolving Credit Facility [Member]	Feb. 04, 2013 Credit Facilities, Amendment No. 2 [Member] Revolving Credit Facility [Member] Minimum [Member]	Feb. 04, 2013 Credit Facilities, Amendment No. 2 [Member] Revolving Credit Facility [Member] Maximum [Member]	Jun. 24, 2013 Credit Facilities, Amendment No. 3 [Member] Revolving Credit Facility [Member]	Feb. 13, 2014 Credit Facilities, Amendment No. 4 [Member] Revolving Credit Facility [Member]	Oct. 08, 2014 Credit Facilities, Amendment No. 5 [Member] Revolving Credit Facility [Member]	Oct. 31, 2014 Revolving Credit Facility [Member] London Interbank Offered Rate (LIBOR) [Member]	Oct. 31, 2014 Revolving Credit Facility [Member]	Apr. 30, 2014 Revolving Credit Facility [Member]	Mar. 09, 2012 Revolving Credit Facility [Member]
Note F - Debt Facilities (Details) [Line Items]
Line of Credit Facility, Interest Rate at Period End										2.40%	2.40%
Line of Credit Facility, Maximum Borrowing Capacity			$ 145,000,000							$ 145,000,000		$ 125,000,000
Contract Term of Contracts Included by Credit Facilities Amendment				36 months	42 months
Line of Credit Facility, Expiration Date						Jun. 24, 2016		Oct. 08, 2014		Oct. 08, 2017
Line of Credit Facility, Additional Borrowing Capacity						55,000,000
Decrease in Pricing Tiers, Percent						0.25%
Maximum Allowable Capital Expenditures By Credit Facilities Amendment							10,000,000
Increase in Pricing Tiers, Percent								0.125%
Line of Credit Facility, Distribution Limitations, Maximum Aggregate Amount of Stock Repurchases	40,000,000							40,000,000		40,000,000
Line of Credit Facility, Distribution Limitations, Percentage of Sum of Borrowing Bases	30.00%							30.00%		30.00%
Debt Instrument, Basis Spread on Variable Rate									2.375%
Line of Credit Facility, Distribution Limitations, Percentage of Consolidated Net income	75.00%									75.00%
Line of Credit Facility, Distribution Limitations, Minimum Percentage of Aggregate Funds Available	12.50%									12.50%
Line of Credit Facility, Remaining Borrowing Capacity										36,100,000
Amortization of Financing Costs and Discounts	$ 93,000	$ 118,000