Consolidated Statements Of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Aug. 31, 2013	Aug. 31, 2012	Aug. 31, 2011
Consolidated Statements Of Operations [Abstract]
Operating revenues	$ 690,848	$ 551,255	$ 478,890
Cost of operating revenues	496,014	402,737	349,105
Gross profit	194,834	148,518	129,785
Operating expenses:
Selling expense	32,937	28,104	27,842
General and administrative expense	43,441	38,198	33,659
Engineering and research expense	11,395	9,481	10,403
Environmental remediation expense		7,225	1,295
Total operating expenses	87,773	83,008	73,199
Operating income	107,061	65,510	56,586
Interest expense	(304)	(492)	(762)
Interest income	496	504	315
Other income (expense), net	54	(414)	375
Earnings before income taxes	107,307	65,108	56,514
Income tax expense	36,737	21,831	19,712
Net earnings	$ 70,570	$ 43,277	$ 36,802
Earnings per share:
Basic	$ 5.50	$ 3.41	$ 2.93
Diluted	$ 5.47	$ 3.38	$ 2.90
Shares used in computing earnings per share:
Basic	12,830	12,704	12,560
Diluted	12,901	12,810	12,692
Cash dividends declared per share	$ 0.475	$ 0.385	$ 0.345