Condensed Consolidated Statements Of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 28, 2017	Feb. 29, 2016	Feb. 28, 2017	Feb. 29, 2016
Condensed Consolidated Statements Of Operations [Abstract]
Operating revenues	$ 124,125	$ 120,573	$ 234,515	$ 242,195
Cost of operating revenues	91,184	88,128	173,200	175,336
Gross profit	32,941	32,445	61,315	66,859
Operating expenses:
Selling expense	10,132	10,363	20,114	20,355
General and administrative expense	10,230	23,028	21,585	32,043
Engineering and research expense	4,057	3,748	8,359	7,407
Total operating expenses	24,419	37,139	50,058	59,805
Operating income (loss)	8,522	(4,694)	11,257	7,054
Other income (expense):
Interest expense	(1,201)	(1,201)	(2,410)	(2,397)
Interest income	171	229	336	393
Other income (expense), net	144	(527)	(212)	(847)
Earnings (loss) before income taxes	7,636	(6,193)	8,971	4,203
Income tax expense (benefit)	2,624	(2,064)	3,086	1,388
Net earnings (loss)	$ 5,012	$ (4,129)	$ 5,885	$ 2,815
Earnings (loss) per share:
Basic	$ 0.47	$ (0.37)	$ 0.55	$ 0.25
Diluted	$ 0.47	$ (0.37)	$ 0.55	$ 0.25
Shares used in computing earnings (loss) per share:
Basic	10,657	11,024	10,647	11,142
Diluted	10,674	11,024	10,670	11,163
Cash dividends declared per share	$ 0.29	$ 0.28	$ 0.58	$ 0.56