Summary of Significant Accounting Policies - ASU update (Details) - USD ($) $ in Thousands		3 Months Ended								4 Months Ended	8 Months Ended	12 Months Ended				32 Months Ended
	Sep. 01, 2018	Aug. 31, 2020	May 31, 2020	Feb. 29, 2020	Nov. 30, 2019	Aug. 31, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Dec. 31, 2017	Aug. 31, 2018	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2020	Sep. 01, 2019
Recently Adopted Accounting Pronouncements
Package of practical expedients												true
Operating lease liability		$ 8,260										$ 8,260				$ 8,260
Operating lease liability, short-term		1,865										1,865				1,865
Operating lease long-term liabilities		6,395										6,395				6,395
Operating lease right-of-use asset (Note 8)		8,821										8,821				8,821
Net sales												261,162	$ 281,351	$ 284,188
Retained earnings		298,266				$ 270,260						298,266	270,260			$ 298,266
Net income		$ 9,008	$ 9,908	$ 7,879	$ 7,362	$ 10,074	$ 8,541	$ 5,273	$ 8,823			34,157	32,711	43,143
Selling, general and administrative expense												$ 49,364	$ 48,707	$ 47,703
Statutory tax rate (as a percent)										35.00%	21.00%	21.00%	21.00%	25.70%		21.00%
ASU 2016-02
Recently Adopted Accounting Pronouncements
Operating lease liability																	$ 9,644
Operating lease liability, short-term																	2,071
Operating lease long-term liabilities																	7,573
Operating lease right-of-use asset (Note 8)																	$ 10,200
ASU 2014-09
Recently Adopted Accounting Pronouncements
Net sales	$ 80
Retained earnings	22
ASU 2014-09 | Restatement adjustment
Recently Adopted Accounting Pronouncements
Net sales	67
Net income	$ 5
ASU 2017-07
Recently Adopted Accounting Pronouncements
Selling, general and administrative expense														$ 654	$ 1,065