Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2020	May 31, 2019	May 31, 2020	May 31, 2019
Income Statement [Abstract]
Operating revenues	$ 123,106	$ 121,054	$ 346,287	$ 342,187
Cost of operating revenues	83,410	91,055	239,111	259,066
Gross profit	39,696	29,999	107,176	83,121
Operating expenses:
Selling expense	7,417	7,515	22,101	23,934
General and administrative expense	13,055	14,695	38,026	46,585
Engineering and research expense	3,396	3,314	10,303	10,547
Total operating expenses	23,868	25,524	70,430	81,066
Operating income	15,828	4,475	36,746	2,055
Other income (expense):
Interest expense	(1,197)	(1,169)	(3,574)	(3,552)
Interest income	408	525	1,412	1,930
Other expense, net	(2,774)	(602)	(4,197)	(591)
Earnings (loss) before income taxes	12,265	3,229	30,387	(158)
Income tax expense (benefit)	2,171	332	6,432	(827)
Net earnings	$ 10,094	$ 2,897	$ 23,955	$ 669
Earnings per share:
Basic	$ 0.93	$ 0.27	$ 2.21	$ 0.06
Diluted	$ 0.93	$ 0.27	$ 2.21	$ 0.06
Shares used in computing earnings per share:
Basic	10,835	10,786	10,818	10,779
Diluted	10,877	10,814	10,854	10,807
Cash dividends declared per share	$ 0.32	$ 0.31	$ 0.94	$ 0.93