Segment Data and Foreign Operations (Details)	1 Months Ended	3 Months Ended			9 Months Ended
	Dec. 31, 2016 USD ($)	May 31, 2017 USD ($)	May 31, 2016 USD ($)	Nov. 30, 2015 USD ($)	May 31, 2017 USD ($) segment	May 31, 2016 USD ($)	Aug. 31, 2016 USD ($)
Segment data
Number of operating segments | segment					2
Revenue		$ 64,901,000	$ 64,236,000		$ 183,566,000	$ 176,638,000
Income before income taxes		17,112,000	12,466,000		44,405,000	34,855,000
Total assets		263,715,000			263,715,000		$ 262,819,000
Interest		158,000	284,000		711,000	794,000
Depreciation					3,859,000	4,282,000
Amortization					6,816,000	5,774,000
Cost of sale of inventory step-up					190,000
Gain on sale of business		2,013,000			2,013,000	1,031,000
Asset Impairment Charges						365,000
Exit and demolition costs			662,000		50,000	871,000
Paterson NJ
Segment data
Gain on sale of business					792,000
RodPack Business
Segment data
Gain on sale of business				$ 1,031,000
Asset Impairment Charges				365,000
Bridgewater MA location
Segment data
Gain on sale of assets	$ 68,000				68,000
Industrial Materials
Segment data
Revenue		53,292,000	47,185,000		149,708,000	134,253,000
Income before income taxes		20,259,000	14,191,000		52,364,000	40,391,000
Total assets		160,163,000			160,163,000		136,003,000
Interest		119,000	213,000		533,000	595,000
Depreciation		959,000	1,007,000		3,023,000	2,952,000
Amortization		1,990,000	1,587,000		5,859,000	4,716,000
Asset Impairment Charges				$ 365,000
Industrial Materials | Resin Designs
Segment data
Cost of sale of inventory step-up					190,000
Industrial Materials | Fiber Optic Cable Components Product Line
Segment data
Income before income taxes					2,013
Gain on sale of business		2,013
Construction Materials
Segment data
Revenue		11,609,000	17,051,000		33,858,000	42,385,000
Income before income taxes		3,647,000	5,662,000		12,411,000	14,785,000
Total assets		36,399,000			36,399,000		38,983,000
Interest		39,000	71,000		178,000	199,000
Depreciation		209,000	240,000		560,000	764,000
Amortization		320,000	351,000		957,000	1,058,000
Reportable segments
Segment data
Income before income taxes		23,906,000	19,853,000		64,775,000	55,176,000
Total assets		196,562,000			196,562,000		174,986,000
Corporate and common costs
Segment data
Income before income taxes		(6,794,000)	(7,387,000)		(20,370,000)	(20,321,000)
Total assets		$ 67,153,000			67,153,000		$ 87,833,000
Corporate and common costs | Resin Designs
Segment data
Acquisition related expenses					584,000
Corporate and common costs | Randolph MA
Segment data
Exit and demolition costs			$ 662,000		$ 50,000	$ 871,000