Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2020
Segment Reporting Information [Line Items]
Cost of services	$ 333,042	$ 234,805	$ 856,288	$ 700,646
Gross profit	72,829	58,320	196,382	159,799
Selling, general and administrative expenses	50,342	44,261	140,783	124,169
Contingent consideration	69	0	142	0
Loss (gain) on sale of assets	(32)	(3)	(24)	(40)
Operating income (loss)	22,450	14,062	55,481	35,670
Depreciation and amortization expense	6,062	3,200	15,910	8,797
Capital expenditures	2,387	802	5,391	3,700
Total assets	715,930	525,325	715,930	525,325	$ 560,528
Revenues	405,871	293,125	1,052,670	860,445
Commercial and Industrial [Member]
Segment Reporting Information [Line Items]
Cost of services	56,308	52,212	159,664	174,712
Gross profit	7,779	4,566	19,036	15,769
Selling, general and administrative expenses	6,781	8,786	19,949	24,660
Loss (gain) on sale of assets	(32)	(6)	(49)	(34)
Operating income (loss)	1,030	(4,214)	(864)	(8,857)
Depreciation and amortization expense	673	692	2,050	2,057
Capital expenditures	525	496	1,190	1,168
Total assets	76,278	71,877	76,278	71,877
Revenues	64,087	56,778	178,700	190,481
Communications [Member]
Segment Reporting Information [Line Items]
Cost of services	95,582	77,792	250,738	225,866
Gross profit	20,636	18,708	58,722	50,913
Selling, general and administrative expenses	10,783	9,316	29,739	27,304
Loss (gain) on sale of assets	(7)	0	(7)	(9)
Operating income (loss)	9,860	9,392	28,990	23,618
Depreciation and amortization expense	341	330	1,035	1,010
Capital expenditures	187	63	452	531
Total assets	141,004	131,796	141,004	131,796
Revenues	116,218	96,500	309,460	276,779
Infrastructure Solutions [Member]
Segment Reporting Information [Line Items]
Cost of services	28,374	22,609	76,999	68,177
Gross profit	10,743	9,333	31,235	24,348
Selling, general and administrative expenses	5,961	5,512	17,787	14,923
Loss (gain) on sale of assets	(1)	3	(1)	3
Operating income (loss)	4,783	3,818	13,449	9,422
Depreciation and amortization expense	1,553	1,683	4,548	4,557
Capital expenditures	1,034	135	1,542	725
Total assets	136,741	126,557	136,741	126,557
Revenues	39,117	31,942	108,234	92,525
Residential [Member]
Segment Reporting Information [Line Items]
Cost of services	152,778	82,192	368,887	231,891
Gross profit	33,671	25,713	87,389	68,769
Selling, general and administrative expenses	22,634	16,767	61,570	46,241
Contingent consideration	69		142
Loss (gain) on sale of assets	8	0	60	0
Operating income (loss)	10,960	8,946	25,617	22,528
Depreciation and amortization expense	3,456	476	8,165	1,117
Capital expenditures	641	108	2,118	977
Total assets	308,411	107,919	308,411	107,919
Revenues	186,449	107,905	456,276	300,660
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Cost of services	0	0	0	0
Gross profit	0	0	0	0
Selling, general and administrative expenses	4,183	3,880	11,738	11,041
Loss (gain) on sale of assets	0	0	(27)	0
Operating income (loss)	(4,183)	(3,880)	(11,711)	(11,041)
Depreciation and amortization expense	39	19	112	56
Capital expenditures	0	0	89	299
Total assets	53,496	87,176	53,496	87,176
Revenues	$ 0	$ 0	$ 0	$ 0