Quarterly Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 129,455	$ 115,813	$ 118,716	$ 106,575	$ 114,717	$ 118,062	$ 151,570	$ 134,150	$ 470,559	$ 518,499
Gross profit	22,472	17,167	17,153	18,271	21,720	21,344	29,685	21,826	75,063	94,575	$ 86,976
Net income (loss)	$ 3,261	$ (2,041)	$ (225)	$ (364)	$ 2,983	$ 3,481	$ 7,421	$ 2,775	$ 631	$ 16,660	$ 9,890
Earnings per share:
Basic (in dollars per share)	$ 0.28	$ (0.17)	$ (0.02)	$ (0.03)	$ 0.26	$ 0.30	$ 0.64	$ 0.24	$ 0.05	$ 1.43	$ 0.85
Diluted (in dollars per share)	$ 0.28	$ (0.17)	$ (0.02)	$ (0.03)	$ 0.25	$ 0.30	$ 0.64	$ 0.24	$ 0.05	$ 1.42	$ 0.85
Separation costs						$ 1,400			$ 0	$ 1,400	$ 11
Benefits received from life insurance policy					$ 500				$ 0	$ 506	$ 0