Condensed Consolidated Statements Of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010
Condensed Consolidated Statements Of Operations [Abstract]
Operating revenues	$ 551,255	$ 478,890	$ 358,440
Cost of operating revenues	402,737	349,105	259,540
Gross profit	148,518	129,785	98,900
Operating expenses:
Selling expense	28,104	27,842	23,070
General and administrative expense	38,198	33,659	29,521
Engineering and research expense	9,481	10,403	7,792
Environmental remediation expense	7,225	1,295	675
Total operating expenses	83,008	73,199	61,058
Operating income	65,510	56,586	37,842
Other (expense) income:
Interest expense	(492)	(762)	(1,557)
Interest income	504	315	352
Other(expense) income, net	(414)	375	145
Earnings before income taxes	65,108	56,514	36,782
Income tax provision	21,831	19,712	11,920
Net earnings	$ 43,277	$ 36,802	$ 24,862
Basic net earnings per share	$ 3.41	$ 2.93	$ 2.00
Diluted net earnings per share	$ 3.38	$ 2.90	$ 1.98
Weighted average shares outstanding	12,704	12,560	12,451
Diluted effect of stock equivalents	106	132	134
Weighted average shares outstanding assuming dilution	12,810	12,692	12,585
Cash dividends per share	$ 0.385	$ 0.345	$ 0.325