Income Taxes (Details) (USD $)	12 Months Ended
	Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010
Income from continuing operations before income taxes [Abstract]
United States	$ 54,304,000	$ 171,329,000	$ 117,104,000
Foreign	(11,348,000)	9,476,000	8,229,000
Income from continuing operations before income taxes	42,956,000	180,805,000	125,333,000
Current [Abstract]
Federal	5,267,000	33,499,000	25,187,000
State	453,000	2,583,000	1,801,000
Foreign	(2,000)	82,000	2,320,000
Total current tax expense	5,718,000	36,164,000	29,308,000
Deferred [Abstract]
Federal	13,166,000	19,164,000	10,466,000
State	(2,748,000)	383,000	812,000
Foreign	(2,097,000)	1,457,000	239,000
Total deferred tax expense	8,321,000	21,004,000	11,517,000
Total income tax expense	14,039,000	57,168,000	40,825,000
Reconciliation of the difference between the federal statutory rate and the Company's effective tax rate [Abstract]
Federal statutory rate	35.00%	35.00%	35.00%
State taxes, net of credits	(5.70%)	0.70%	0.70%
Foreign income taxed at different rates	4.20%	(0.60%)	(0.60%)
Section 199 deduction	(0.30%)	(1.00%)	(2.40%)
Non-deductible officers’ compensation	1.50%	0.30%	1.00%
Noncontrolling interests	(2.20%)	(1.00%)	(1.10%)
Research and development credits	(2.00%)	(0.50%)	0.00%
Foreign interest income	0.70%	0.00%	0.00%
Other	1.50%	(1.30%)	0.00%
Effective tax rate	32.70%	31.60%	32.60%
Deferred tax assets [Abstract]
Environmental liabilities	11,165,000	9,727,000
Employee benefit accruals	9,784,000	12,547,000
State income tax and other	5,384,000	2,948,000
Net operating loss carryforwards	5,699,000	988,000
State credit carryforwards	4,374,000	2,294,000
Inventory valuation methods	1,560,000	4,321,000
Valuation allowance	(795,000)	(589,000)
Total deferred tax assets	37,171,000	32,236,000
Deferred tax liabilities [Abstract]
Accelerated depreciation and basis differences	110,996,000	101,457,000
Prepaid expense acceleration	2,365,000	2,287,000
Foreign currency translation adjustment	1,987,000	2,086,000
Total deferred tax liabilities	115,348,000	105,830,000
Net deferred tax liability	78,177,000	73,594,000
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, as of the beginning of the year	303,000	1,631,000	3,372,000
Reductions for tax positions of prior years	(143,000)	(75,000)	(274,000)
Settlements with tax authorities	0	(875,000)	(315,000)
Additions for tax positions of the current year	331,000	160,000	0
Reductions for lapse of statutes	0	(538,000)	(1,152,000)
Unrecognized tax benefits, as of the end of the year	491,000	303,000	1,631,000
Foreign Country [Member]
Deferred tax liabilities [Abstract]
Operating Loss Carryforwards	18,000,000
Foreign Country [Member] | Minimum [Member]
Deferred tax liabilities [Abstract]
Operating Loss Carryforwards, Expiration Dates	2013
Foreign Country [Member] | Maximum [Member]
Deferred tax liabilities [Abstract]
Operating Loss Carryforwards, Expiration Dates	2031
State and Local Jurisdiction [Member] | Minimum [Member]
Deferred tax liabilities [Abstract]
Tax Credit Carryforward, Expiration Dates	2013
State and Local Jurisdiction [Member] | Maximum [Member]
Deferred tax liabilities [Abstract]
Tax Credit Carryforward, Expiration Dates	2021
Deferred Tax Liabilities Correction [Member]
Reconciliation of the difference between the federal statutory rate and the Company's effective tax rate [Abstract]
Correction of error resulting in reduction of income tax expense		$ 3,000,000