Revenue Recognition (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 1,536,493	$ 1,190,856	$ 1,076,996
Unbilled Receivables, Current	20,445
Contract with Customer, Liability, Revenue Recognized	47,906	34,035
Revenue, Remaining Performance Obligation, Amount	713,274
Performance Obligation Next 12 Months	650,500
Communications [Member]
Disaggregation of Revenue [Line Items]
Revenues	445,968	395,141	321,246
Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	687,347	411,790	313,336
Infrastructure Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenues	146,980	128,379	136,790
Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	256,198	255,546	305,624
Fixed-price Contract [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,397,921	1,085,143	957,894
Fixed-price Contract [Member] | Communications [Member]
Disaggregation of Revenue [Line Items]
Revenues	327,496	309,567	229,143
Fixed-price Contract [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	687,347	411,790	313,336
Fixed-price Contract [Member] | Infrastructure Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenues	139,532	121,922	129,096
Fixed-price Contract [Member] | Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	243,546	241,864	286,319
Time-and-materials Contract [Member]
Disaggregation of Revenue [Line Items]
Revenues	138,572	105,713	119,102
Time-and-materials Contract [Member] | Communications [Member]
Disaggregation of Revenue [Line Items]
Revenues	118,472	85,574	92,103
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	7,448	6,457	7,694
Time-and-materials Contract [Member] | Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	12,652	13,682	19,305
industrial Services [Member] | Infrastructure Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenues	44,427	40,701	48,948
Custom Power Solutions [Member] | Infrastructure Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenues	102,553	87,678	87,842
Single Family Contracts [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	454,449	239,140	212,358
Multi Family and Other [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 232,898	$ 172,650	$ 100,978