Quarterly Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 114,717	$ 118,062	$ 151,570	$ 134,150	$ 148,504	$ 135,588	$ 123,737	$ 109,351	$ 518,499	$ 517,180
Gross profit	21,720	21,344	29,685	21,826	28,555	23,715	20,075	14,631	94,575	86,976	$ 65,355
Net income	$ 2,983	$ 3,481	$ 7,421	$ 2,775	$ 6,538	$ 5,089	$ 958	$ (2,695)	$ 16,660	$ 9,890	$ (7,152)
Earnings (loss) per share:
Basic (in dollars per share)	$ 0.26	$ 0.30	$ 0.64	$ 0.24	$ 0.56	$ 0.44	$ 0.08	$ (0.23)	$ 1.43	$ 0.85	$ (0.62)
Diluted (in dollars per share)	$ 0.25	$ 0.30	$ 0.64	$ 0.24	$ 0.56	$ 0.44	$ 0.08	$ (0.23)	$ 1.42	$ 0.85	$ (0.62)
Separation costs		$ 1,400							$ 1,400	$ 11	$ 787
Proceeds from life insurance policy	$ 500								0	0	1,861
Insurance settlement proceeds						$ 1,000			$ 0	$ 950	$ 0