Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues	$ 293,607	$ 282,633	$ 256,914	$ 243,842	$ 240,275	$ 232,576	$ 205,677	$ 198,300	$ 1,076,996	$ 876,828	$ 810,744
Cost of services									894,893	726,866	670,246
Gross profit	50,870	$ 46,397	$ 43,235	$ 41,601	40,521	$ 42,537	$ 33,840	$ 33,064	182,103	149,962	140,498
Selling, general and administrative expenses									140,575	123,920	120,370
Contingent consideration									(374)	103	(145)
Loss (gain) on sale of assets									52	(15)	(69)
Operating income (loss)									41,850	25,954	20,342
Depreciation and amortization									9,557	8,860	9,634
Capital expenditures									6,300	4,563	4,589
Total assets	445,258				421,994				445,258	421,994	424,494
Commercial and Industrial [Member]
Segment Reporting Information [Line Items]
Revenues									305,624	274,299	227,606
Cost of services									275,722	244,656	208,619
Gross profit									29,902	29,643	18,987
Selling, general and administrative expenses									27,815	27,031	20,170
Contingent consideration									0	(100)	0
Loss (gain) on sale of assets									(30)	(37)	(32)
Operating income (loss)									2,117	2,749	(1,151)
Depreciation and amortization									2,563	2,197	1,648
Capital expenditures									2,402	2,216	1,241
Total assets	82,050				89,729				82,050	89,729	84,756
Communications [Member]
Segment Reporting Information [Line Items]
Revenues									321,246	219,655	225,275
Cost of services									264,746	179,518	187,419
Gross profit									56,500	40,137	37,856
Selling, general and administrative expenses									31,850	26,003	24,219
Contingent consideration									(97)	(85)	0
Loss (gain) on sale of assets									(6)	(4)	(1)
Operating income (loss)									24,753	14,223	13,638
Depreciation and amortization									1,513	1,247	740
Capital expenditures									973	647	2,046
Total assets	109,263				80,528				109,263	80,528	63,917
Infrastructure Solutions [Member]
Segment Reporting Information [Line Items]
Revenues									136,790	97,163	83,824
Cost of services									105,863	75,337	63,399
Gross profit									30,927	21,826	20,425
Selling, general and administrative expenses									18,664	18,293	17,859
Contingent consideration									(277)	288	(145)
Loss (gain) on sale of assets									105	18	(79)
Operating income (loss)									12,435	3,227	2,790
Depreciation and amortization									4,528	4,672	6,412
Capital expenditures									1,377	735	538
Total assets	116,867				109,506				116,867	109,506	106,114
Residential [Member]
Segment Reporting Information [Line Items]
Revenues									313,336	285,711	274,039
Cost of services									248,562	227,355	210,809
Gross profit									64,774	58,356	63,230
Selling, general and administrative expenses									46,864	41,401	43,689
Contingent consideration									0	0	0
Loss (gain) on sale of assets									(17)	8	43
Operating income (loss)									17,927	16,947	19,498
Depreciation and amortization									852	637	565
Capital expenditures									1,412	932	561
Total assets	63,903				55,176				63,903	55,176	51,994
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Revenues									0	0	0
Cost of services									0	0	0
Gross profit									0	0	0
Selling, general and administrative expenses									15,382	11,192	14,433
Contingent consideration									0	0	0
Loss (gain) on sale of assets									0	0	0
Operating income (loss)									(15,382)	(11,192)	(14,433)
Depreciation and amortization									101	107	269
Capital expenditures									136	33	203
Total assets	$ 73,175				$ 87,055				$ 73,175	$ 87,055	$ 117,713