Loans Payable and Long-Term Debt (Narrative) (Details)		3 Months Ended	12 Months Ended				28 Months Ended	40 Months Ended
	Jan. 25, 2016 USD ($)	Apr. 30, 2016 USD ($)	Apr. 30, 2016 USD ($)	Apr. 30, 2015 USD ($)	Apr. 30, 2014 USD ($)	Dec. 31, 2005 loan	Apr. 30, 2015 USD ($) lease	Apr. 30, 2015 USD ($) lease
Debt Instrument [Line Items]
LIBOR rate		0.495%	0.495%
Spread on interest rate			1.50%
Required maximum ratio of total liabilities to tangible net worth under agreement			140.00%
Required minimum ratio of cash flow to fixed charges under agreement			150.00%
Ratio of total liabilities to tangible net worth			66.70%
Ratio cash flow to fixed charges			341.00%
Debt, outstanding balance		$ 24,052,000	$ 24,052,000
New Markets Tax Credit Investment	$ 2,300,000
New Markets Tax Credit, Recapture Period	7 years
Interest paid under agreement and capital leases			500,000	$ 500,000	$ 700,000
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
LIBOR rate	1.20%
Debt instrument, face amount	$ 6,600,000
Loan term	30 years
Deferred Finance Costs, Net	$ 300,000
Deferred Finance Costs, Amortization Period	30 years
Other Noncurrent Assets [Member]
Debt Instrument [Line Items]
Notes, Loans and Financing Receivable, Net, Noncurrent	$ 4,300,000
Long-term Debt [Member]
Debt Instrument [Line Items]
Amount drawn on loan		3,200,000	$ 3,200,000
Eligible Accounts Receivable [Member]
Debt Instrument [Line Items]
Advanced rate			75.00%
Eligible Pre Bill Reserves [Member]
Debt Instrument [Line Items]
Advanced rate			50.00%
Equipment Value [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 20,000,000	$ 20,000,000
Board Of County Commissioners Of Garrett County [Member]
Debt Instrument [Line Items]
Fixed interest rate		3.00%	3.00%
Value of land and associated site improvements		$ 3,500,000	$ 3,500,000
Accrued interest		1,600,000	1,600,000
Debt, outstanding balance		0	$ 0	1,300,000			$ 1,300,000	$ 1,300,000
Board Of County Commissioners Of Garrett County [Member] | Other Income (Expense) [Member]
Debt Instrument [Line Items]
Loss on loan settlement		$ 1,900,000
Allegany County, Maryland Site [Member]
Debt Instrument [Line Items]
Fixed interest rate		3.00%	3.00%
Debt, outstanding balance		$ 2,200,000	$ 2,200,000	2,200,000			2,200,000	$ 2,200,000
Number of loan agreements | loan						2
First American Financial Bancorp [Member]
Debt Instrument [Line Items]
Number of capitalized lease agreements | lease								18
Capital lease obligations incurred								$ 2,500,000
Capital lease term								48 months
Market interest rate		6.50%	6.50%
Capital lease agreement		$ 1,100,000	$ 1,100,000	1,300,000			$ 1,300,000	$ 1,300,000
e-Plus Group [Member]
Debt Instrument [Line Items]
Number of capitalized lease agreements | lease							17
Capital lease obligations incurred							$ 1,900,000
Capital lease term							51 months
Market interest rate		6.50%	6.50%
Capital lease agreement		$ 1,000,000	$ 1,000,000	1,000,000			$ 1,000,000	1,000,000
West Virginia Economic Development Authority [Member]
Debt Instrument [Line Items]
Fixed interest rate		2.00%	2.00%
Debt, outstanding balance		$ 5,000,000	$ 5,000,000	5,600,000			5,600,000	5,600,000
Capital lease agreement		10,000,000	10,000,000
West Virginia Economic Development Authority [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Debt instrument, face amount		$ 1,500,000	$ 1,500,000
Debt instrument, interest rate, stated percentage		3.00%	3.00%
Wells Fargo [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 35,000,000	$ 35,000,000
Amount oustanding		10,000,000	10,000,000	$ 10,000,000			$ 10,000,000	$ 10,000,000
Remaining availability		$ 25,000,000	$ 25,000,000