Quarterly Results of Operations (Schedule of Quarterly Results) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Aug. 31, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Operating revenues	$ 101,885	$ 121,054	$ 109,182	$ 111,951	$ 123,269	$ 169,571	$ 130,339	$ 124,526	$ 444,072	$ 547,705	$ 517,985
Cost of operating revenues	70,398	91,055	84,708	83,303	90,998	118,093	95,023	92,129	329,464	396,243	372,973
Earnings (loss) before income taxes	2,265	3,229	(5,068)	1,681	5,940	17,445	5,676	4,792	2,107	33,853	35,715
Net earnings (loss)	$ 1,503	$ 2,897	$ (3,440)	$ 1,212	$ 4,978	$ 10,379	$ 1,735	$ 3,185	$ 2,172	$ 20,277	$ 23,179
Diluted net earnings (loss) per share	$ 0.14	$ 0.27	$ (0.32)	$ 0.11	$ 0.46	$ 0.96	$ 0.16	$ 0.30	$ 0.20	$ 1.88	$ 2.17