Benefits and Pension Plans - Fair Value (Details) - USD ($) $ in Thousands	Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2015	Aug. 31, 2014
Benefits and pension plans
Fair value of plan assets	$ 9,003	$ 8,440	$ 8,120	$ 8,818
Equity securities
Benefits and pension plans
Fair value of plan assets	3,589	3,866
Debt securities
Benefits and pension plans
Fair value of plan assets	5,336	4,499
Other
Benefits and pension plans
Fair value of plan assets	78	75
Quoted prices in active markets (Level 1)
Benefits and pension plans
Fair value of plan assets		8,440
Quoted prices in active markets (Level 1) | Equity securities
Benefits and pension plans
Fair value of plan assets		3,866
Quoted prices in active markets (Level 1) | Debt securities
Benefits and pension plans
Fair value of plan assets		4,499
Quoted prices in active markets (Level 1) | Other
Benefits and pension plans
Fair value of plan assets		$ 75
Significant other observable inputs (Level 2)
Benefits and pension plans
Fair value of plan assets	9,003
Significant other observable inputs (Level 2) | Equity securities
Benefits and pension plans
Fair value of plan assets	3,589
Significant other observable inputs (Level 2) | Debt securities
Benefits and pension plans
Fair value of plan assets	5,336
Significant other observable inputs (Level 2) | Other
Benefits and pension plans
Fair value of plan assets	$ 78