Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019
Revenue Recognition and Deferred Revenue [Abstract]
Capitalized Contract Cost, Net	$ 69		$ 69
Unbilled Receivables, Current	8,324		8,324
Estimated profits on contracts in process	868,267		868,267		$ 761,401
Billings to Date	(898,620)		(898,620)		(772,104)
Contract with Customer, Asset, Net, Current	(30,353)		(30,353)		(10,703)
Costs and estimated earnings in excess of billings	25,821		25,821		29,860
Billings in excess of costs and estimated earnings	(56,174)		(56,174)		$ (40,563)
Contract with Customer, Liability, Revenue Recognized	19,661	$ 18,472	29,692	$ 28,816
Performance Obligation Next 12 Months	451		451
Revenue, Remaining Performance Obligation, Amount	523		523
Disaggregation of Revenue [Line Items]
Revenues	293,125	282,633	860,445	783,389
Contract with Customer, Liability, Revenue Recognized	19,661	18,472	29,692	28,816
Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	56,778	75,370	190,481	227,928
Communications [Member]
Disaggregation of Revenue [Line Items]
Revenues	96,500	90,438	276,779	230,200
Infrastructure Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenues	31,942	36,109	92,525	100,038
Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	107,905	80,716	300,660	225,223
Fixed-price Contract [Member]
Disaggregation of Revenue [Line Items]
Revenues	272,021	251,096	781,769	694,940
Fixed-price Contract [Member] | Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	53,811	70,917	180,425	213,214
Fixed-price Contract [Member] | Communications [Member]
Disaggregation of Revenue [Line Items]
Revenues	79,801	65,219	213,205	162,650
Fixed-price Contract [Member] | Infrastructure Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenues	30,504	34,244	87,479	93,853
Fixed-price Contract [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	107,905	80,716	300,660	225,223
Time-and-materials Contract [Member]
Disaggregation of Revenue [Line Items]
Revenues	21,104	31,537	78,676	88,449
Time-and-materials Contract [Member] | Commercial and Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,967	4,453	10,056	14,714
Time-and-materials Contract [Member] | Communications [Member]
Disaggregation of Revenue [Line Items]
Revenues	16,699	25,219	63,574	67,550
Time-and-materials Contract [Member] | Infrastructure Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,438	1,865	5,046	6,185
Time-and-materials Contract [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
industrial Services [Member] | Infrastructure Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenues	9,753	12,339	31,588	36,707
Custom Power Solutions [Member] | Infrastructure Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenues	22,189	23,770	60,937	63,331
Single Family Contracts [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	62,239	54,200	176,071	156,168
Multi Family and Other [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 45,666	$ 26,516	$ 124,589	$ 69,055