Revenue Recognition (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenues	$ 3,371,468	$ 2,884,358	$ 2,377,227
Contract with Customer, Liability, Revenue Recognized	147,995	98,564
Capitalized Contract Cost, Impairment Loss	0	0	0
Unbilled Receivables, Current	16,461
Contract with Customer, Liability, Revenue Recognized	147,995	98,564
Performance Obligation Next 12 Months	1,029,713
Revenue, Remaining Performance Obligation, Amount	1,686,583
Communications [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,140,640	776,474	600,776
Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,304,369	1,388,840	1,279,504
Infrastructure Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenues	498,724	351,096	217,353
Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	427,735	367,948	279,594
Fixed-price Contract [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,937,979	2,596,151	2,135,894
Fixed-price Contract [Member] | Communications [Member]
Disaggregation of Revenue [Line Items]
Revenues	803,930	554,160	404,684
Fixed-price Contract [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,304,369	1,388,840	1,279,504
Fixed-price Contract [Member] | Infrastructure Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenues	457,587	336,786	210,547
Fixed-price Contract [Member] | Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	372,093	316,365	241,159
Time-and-materials Contract [Member]
Disaggregation of Revenue [Line Items]
Revenues	433,489	288,207	241,333
Time-and-materials Contract [Member] | Communications [Member]
Disaggregation of Revenue [Line Items]
Revenues	336,710	222,314	196,092
Time-and-materials Contract [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Time-and-materials Contract [Member] | Infrastructure Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenues	41,137	14,310	6,806
Time-and-materials Contract [Member] | Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	55,642	51,583	38,435
industrial Services [Member] | Infrastructure Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenues	98,262	53,291	46,091
Custom Power Solutions [Member] | Infrastructure Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenues	400,462	297,805	171,262
Single Family Contracts [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	665,610	732,334	717,386
Multi Family and Other [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	312,961	331,595	318,233
Single Family Plumbing HVAC | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 325,798	$ 324,911	$ 243,885