Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Income Statement [Abstract]
Operating revenues	$ 109,182	$ 130,339	$ 221,133	$ 254,865
Cost of operating revenues	84,708	95,023	168,011	187,152
Gross profit	24,474	35,316	53,122	67,713
Operating expenses:
Selling expense	8,437	10,020	16,419	20,245
General and administrative expense	16,832	14,086	31,890	26,004
Engineering and research expense	3,665	3,919	7,233	7,972
Total operating expenses	28,934	28,025	55,542	54,221
Operating income (loss)	(4,460)	7,291	(2,420)	13,492
Other income (expense):
Interest expense	(1,178)	(1,095)	(2,383)	(2,331)
Interest income	751	311	1,405	686
Other (expense) income, net	(181)	(831)	11	(1,379)
Earnings (loss) before income taxes	(5,068)	5,676	(3,387)	10,468
Income tax expense (benefit)	(1,628)	3,941	(1,159)	5,548
Net earnings (loss)	$ (3,440)	$ 1,735	$ (2,228)	$ 4,920
Earnings (loss) per share:
Basic	$ (0.32)	$ 0.16	$ (0.21)	$ 0.46
Diluted	$ (0.32)	$ 0.16	$ (0.21)	$ 0.46
Shares used in computing earnings (loss) per share:
Basic	10,786	10,743	10,776	10,724
Diluted	10,786	10,765	10,776	10,752
Cash dividends declared per share	$ 0.31	$ 0.30	$ 0.62	$ 0.60