Condensed Consolidated Statements Of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Nov. 30, 2014	Nov. 30, 2013
Condensed Consolidated Statements Of Operations [Abstract]
Operating revenues	$ 134,845us-gaap_Revenues	$ 147,671us-gaap_Revenues
Cost of operating revenues	97,931us-gaap_CostOfRevenue	107,520us-gaap_CostOfRevenue
Gross profit	36,914us-gaap_GrossProfit	40,151us-gaap_GrossProfit
Operating expenses:
Selling expense	9,417us-gaap_SellingExpense	9,756us-gaap_SellingExpense
General and administrative expense	12,871us-gaap_GeneralAndAdministrativeExpense	11,743us-gaap_GeneralAndAdministrativeExpense
Engineering and research expense	2,724us-gaap_ResearchAndDevelopmentExpense	2,660us-gaap_ResearchAndDevelopmentExpense
Total operating expenses	25,012us-gaap_OperatingExpenses	24,159us-gaap_OperatingExpenses
Operating income	11,902us-gaap_OperatingIncomeLoss	15,992us-gaap_OperatingIncomeLoss
Other income (expense):
Interest expense	(71)us-gaap_InterestExpense	(39)us-gaap_InterestExpense
Interest income	172us-gaap_InvestmentIncomeInterest	135us-gaap_InvestmentIncomeInterest
Other expense, net	(342)us-gaap_OtherNonoperatingIncomeExpense	(271)us-gaap_OtherNonoperatingIncomeExpense
Earnings before income taxes	11,661	15,817
Income tax expense	4,093us-gaap_IncomeTaxExpenseBenefit	5,583us-gaap_IncomeTaxExpenseBenefit
Net earnings	$ 7,568us-gaap_NetIncomeLoss	$ 10,234us-gaap_NetIncomeLoss
Earnings per share:
Basic	$ 0.62us-gaap_EarningsPerShareBasic	$ 0.79us-gaap_EarningsPerShareBasic
Diluted	$ 0.62us-gaap_EarningsPerShareDiluted	$ 0.79us-gaap_EarningsPerShareDiluted
Shares used in computing earnings per share:
Basic	12,224	12,889
Diluted	12,274	12,951
Cash dividends declared per share	$ 0.270	$ 0.130

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