Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Apr. 30, 2012	Apr. 30, 2011
Assets [Abstract]
Cash and cash equivalents	$ 55,919	$ 59,572
Receivables	21,700	20,154
Inventories	170,794	159,200
Prepaid expenses	1,298	1,180
Deferred income taxes	13,143	10,405
Income tax receivable	16,424	43,376
Total current assets	279,278	293,887
Property and equipment, at cost [Abstract]
Land	381,756	348,456
Buildings and leasehold improvements	807,795	724,170
Machinery and equipment	1,035,651	907,483
Leasehold interest in property and equipment	14,545	14,538
Gross property and equipment	2,239,747	1,994,647
Less accumulated depreciation and amortization	860,998	777,342
Net property and equipment	1,378,749	1,217,305
Other assets, net of amortization	12,403	11,721
Goodwill	104,385	88,042
Total assets	1,774,815	1,610,955
Liabilities and Shareholders' Equity [Abstract]
Notes payable to bank		600
Current maturities of long-term debt	10,737	1,167
Accounts payable	211,165	215,675
Accounts expenses [Abstract]
Wages and related taxes	15,010	13,014
Property taxes	19,111	17,283
Insurance	23,701	22,129
Other	26,917	24,632
Total current liabilities	306,641	294,500
Long-term debt, net of current maturities	667,930	678,680
Deferred income taxes	260,405	203,078
Deferred compensation	14,698	13,858
Other long-term liabilities	19,100	16,943
Total liabilities	1,268,774	1,207,059
Commitments and contingencies
Shareholders' equity:
Preferred stock, no par value, none issued
Common stock, no par value, 38,140,309 and 37,966,709 shares issued and outstanding at April 30, 2012 and 2011, respectively	12,199	3,996
Retained earnings	493,842	399,900
Total shareholders' equity	506,041	403,896
Total liabilities and shareholders' equity	$ 1,774,815	$ 1,610,955