Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Segment Reporting Information [Line Items]
Cost of services	$ 267,087	$ 240,013	$ 523,246	$ 465,841
Gross profit	64,874	51,264	123,553	101,479
Selling, general and administrative expenses	47,655	42,036	90,441	79,908
Contingent consideration	73		73	0
Loss (gain) on sale of assets	18	(1)	8	(37)
Operating income (loss)	17,128	9,229	33,031	21,608
Depreciation and amortization expense	5,828	3,235	9,848	5,597
Capital expenditures	1,822	1,507	3,004	2,898
Total assets	615,652	526,344	615,652	526,344	$ 560,528
Revenues	331,961	291,277	646,799	567,320
Commercial and Industrial [Member]
Segment Reporting Information [Line Items]
Cost of services	46,441	61,492	103,356	122,500
Gross profit	5,582	4,468	11,257	11,203
Selling, general and administrative expenses	6,744	8,586	13,168	15,874
Loss (gain) on sale of assets	(8)	(1)	(17)	(28)
Operating income (loss)	(1,154)	(4,117)	(1,894)	(4,643)
Depreciation and amortization expense	683	689	1,377	1,365
Capital expenditures	397	212	665	672
Total assets	69,405	75,075	69,405	75,075
Revenues	52,023	65,960	114,613	133,703
Communications [Member]
Segment Reporting Information [Line Items]
Cost of services	75,339	79,352	155,156	148,074
Gross profit	19,547	16,638	38,086	32,205
Selling, general and administrative expenses	9,615	9,419	18,956	17,988
Loss (gain) on sale of assets	0	0	0	(9)
Operating income (loss)	9,932	7,219	19,130	14,226
Depreciation and amortization expense	347	343	694	680
Capital expenditures	133	186	265	468
Total assets	128,568	126,871	128,568	126,871
Revenues	94,886	95,990	193,242	180,279
Infrastructure Solutions [Member]
Segment Reporting Information [Line Items]
Cost of services	25,161	22,055	48,625	45,568
Gross profit	9,555	7,245	20,492	15,015
Selling, general and administrative expenses	6,242	4,918	11,853	9,411
Loss (gain) on sale of assets	(26)	0	(27)	0
Operating income (loss)	3,339	2,327	8,666	5,604
Depreciation and amortization expense	1,554	1,754	2,995	2,874
Capital expenditures	163	153	508	590
Total assets	134,037	127,426	134,037	127,426
Revenues	34,716	29,300	69,117	60,583
Residential [Member]
Segment Reporting Information [Line Items]
Cost of services	120,146	77,114	216,109	149,699
Gross profit	30,190	22,913	53,718	43,056
Selling, general and administrative expenses	21,609	15,754	38,936	29,474
Contingent consideration	73		73
Loss (gain) on sale of assets	52	0	52	0
Operating income (loss)	8,456	7,159	14,657	13,582
Depreciation and amortization expense	3,205	431	4,709	641
Capital expenditures	1,040	657	1,477	869
Total assets	215,399	101,246	215,399	101,246
Revenues	150,336	100,027	269,827	192,755
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	3,445	3,359	7,528	7,161
Loss (gain) on sale of assets	0	0	0	0
Operating income (loss)	(3,445)	(3,359)	(7,528)	(7,161)
Depreciation and amortization expense	39	18	73	37
Capital expenditures	89	299	89	299
Total assets	68,243	95,726	68,243	95,726
Revenues	$ 0	$ 0	$ 0	$ 0