Accumulated Other Comprehensive Income - Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2016	May 31, 2016	Feb. 29, 2016	Nov. 30, 2015	Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2015
Accumulated other comprehensive income
Selling, general and administrative expenses									$ (47,736)	$ (44,574)	$ (46,015)
Cost of products and services sold									(146,036)	(144,438)	(149,202)
Tax expense (benefit)									(18,878)	(17,303)	(14,813)
Net Income	$ 11,413	$ 11,855	$ 8,383	$ 10,363	$ 10,855	$ 7,531	$ 6,972	$ 7,449	42,014	32,807	26,318
Net income (loss)									42,014	32,807	$ 26,413
Reclassification out of accumulated other comprehensive income (loss)
Accumulated other comprehensive income
Net income (loss)									846	670
Restricted investments | Reclassification out of accumulated other comprehensive income (loss)
Accumulated other comprehensive income
Selling, general and administrative expenses									(127)	(67)
Tax expense (benefit)									39	23
Net income (loss)									(88)	(44)
Change in funded status of pension plan | Reclassification out of accumulated other comprehensive income (loss)
Accumulated other comprehensive income
Selling, general and administrative expenses									1,255	991
Cost of products and services sold									98	106
Tax expense (benefit)									(419)	(383)
Net income (loss)									$ 934	$ 714