Revenue Recognition (Summary of Impacts of ASU on Condensed Consolidated Statement of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Statement of Earnings
Operating revenues	$ 109,182	$ 130,339	$ 221,133	$ 254,865
Operating income	(4,460)	$ 7,291	(2,420)	$ 13,492
ASC Topic 606 Adjustments [Member] | ASC Topic 606 [Member]
Statement of Earnings
Operating revenues	(178)		(6,346)
Operating income	(111)		(3,391)
Balance Without Adoption of ASC Topic 606 [Member] | ASC Topic 606 [Member]
Statement of Earnings
Operating revenues	109,004		214,787
Operating income	$ (4,571)		$ (5,811)