Quarterly Results of Operations (Schedule of Quarterly Results) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Aug. 31, 2020	May 31, 2020	Feb. 29, 2020	Nov. 30, 2019	Aug. 31, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Operating revenues	$ 128,405	$ 123,106	$ 113,788	$ 109,393	$ 101,885	$ 121,054	$ 109,182	$ 111,951	$ 474,692	$ 444,072	$ 547,705
Cost of operating revenues	83,038	83,410	80,382	75,319	70,398	91,055	84,708	83,303	322,149	329,464	396,243
Earnings (loss) before income taxes	18,456	12,265	6,867	11,255	2,265	3,229	(5,068)	1,681	48,843	2,107	33,853
Net earnings (loss)	$ 14,674	$ 10,094	$ 5,516	$ 8,345	$ 1,503	$ 2,897	$ (3,440)	$ 1,212	$ 38,629	$ 2,172	$ 20,277
Diluted net earnings (loss) per share	$ 1.35	$ 0.93	$ 0.51	$ 0.77	$ 0.14	$ 0.27	$ (0.32)	$ 0.11	$ 3.56	$ 0.20	$ 1.88