Equity method investments - summarized financial information of equity method investees (Details) - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2015
Equity Method Investment, Summarized Financial Information [Abstract]
Current assets	$ 29,707,000		$ 27,066,000
Non-current assets		$ 12,999,000	12,496,000
Current liabilities		30,559,000	28,569,000
Non-current liabilities		7,362,000	6,891,000
Shareholders’ equity		4,785,000	4,102,000
Income Statement [Abstract]
Sales	164,844,000	55,153,000	20,905,000
Gross profit	5,958,000	2,672,000	3,794,000
Net earnings	1,040,000	534,000	791,000
Share of earnings from equity method investments	$ 143,000	$ 81,000	$ 339,000