Quarterly Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 208,641	$ 192,365	$ 171,444	$ 126,858	$ 162,676	$ 135,483	$ 127,854	$ 106,569	$ 699,308	$ 532,582
Gross profit	51,982	42,670	33,437	19,464	33,440	19,059	19,083	13,436	147,553	85,018	$ 75,063
Net income (loss)	$ 26,436	$ 18,454	$ 8,473	$ 1,162	$ 8,739	$ 9,061	$ (1,217)	$ (2,846)	$ 54,525	$ 13,737	$ 631
Earnings (loss) per share
Basic (in dollars per share)	$ 2.22	$ 1.55	$ 0.71	$ 0.10	$ 0.74	$ 0.77	$ (0.10)	$ (0.24)	$ 4.59	$ 1.16	$ 0.05
Diluted (in dollars per share)	$ 2.17	$ 1.52	$ 0.70	$ 0.10	$ 0.73	$ 0.76	$ (0.10)	$ (0.24)	$ 4.50	$ 1.15	$ 0.05
Change in contract estimates due to project cancellations	$ 1,000	$ 1,700	$ 1,600						$ 700
Decrease in valuation allowance	$ (1,900)					$ 5,900			(1,800)
Gain on sale of non-core business						$ 2,000			0	$ 2,006	$ 0
Revenue recognized related to settlement of a claim for cost overruns from prior years					$ 2,500				$ 70,500