Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues	$ 282,633	$ 232,576	$ 783,389	$ 636,553
Cost of services	236,236	190,039	652,156	527,112
Gross profit	46,397	42,537	131,233	109,441
Selling, general and administrative expenses	36,333	32,372	103,489	92,108
Contingent consideration	(163)	81	(278)	152
Loss (gain) on sale of assets	(8)	(5)	87	(39)
Operating income (loss)	10,235	10,089	27,935	17,220
Depreciation and amortization expense	2,354	2,437	7,200	6,706
Capital expenditures	1,243	1,056	5,172	3,383
Total assets	438,364	395,963	438,364	395,963	$ 421,994
Commercial and Industrial [Member]
Segment Reporting Information [Line Items]
Revenues	75,370	78,156	227,928	196,747
Cost of services	69,171	67,839	204,263	175,066
Gross profit	6,199	10,317	23,665	21,681
Selling, general and administrative expenses	6,827	6,980	20,906	19,624
Contingent consideration	0	0	0	0
Loss (gain) on sale of assets	(4)	(6)	(8)	(35)
Operating income (loss)	(624)	3,343	2,767	2,092
Depreciation and amortization expense	652	548	1,907	1,632
Capital expenditures	507	715	1,974	1,638
Total assets	81,693	86,012	81,693	86,012
Communications [Member]
Segment Reporting Information [Line Items]
Revenues	90,438	54,368	230,200	159,071
Cost of services	75,044	43,436	190,895	129,667
Gross profit	15,394	10,932	39,305	29,404
Selling, general and administrative expenses	8,406	7,193	23,006	19,478
Contingent consideration	0	0	0	0
Loss (gain) on sale of assets	0	0	0	(9)
Operating income (loss)	6,988	3,739	16,299	9,935
Depreciation and amortization expense	339	595	1,180	1,030
Capital expenditures	74	119	767	592
Total assets	111,270	67,270	111,270	67,270
Infrastructure Solutions [Member]
Segment Reporting Information [Line Items]
Revenues	36,109	24,856	100,038	70,407
Cost of services	27,671	18,701	78,227	54,543
Gross profit	8,438	6,155	21,811	15,864
Selling, general and administrative expenses	4,937	4,568	14,103	13,762
Contingent consideration	(163)	81	(278)	152
Loss (gain) on sale of assets	(4)	1	97	6
Operating income (loss)	3,668	1,505	7,889	1,944
Depreciation and amortization expense	1,122	1,120	3,391	3,503
Capital expenditures	311	112	1,133	457
Total assets	118,143	102,233	118,143	102,233
Residential [Member]
Segment Reporting Information [Line Items]
Revenues	80,716	75,196	225,223	210,328
Cost of services	64,350	60,063	178,771	167,836
Gross profit	16,366	15,133	46,452	42,492
Selling, general and administrative expenses	11,812	10,941	34,136	30,995
Contingent consideration	0	0	0	0
Loss (gain) on sale of assets	0	0	(2)	(1)
Operating income (loss)	4,554	4,192	12,318	11,498
Depreciation and amortization expense	218	156	644	452
Capital expenditures	329	110	1,174	696
Total assets	57,866	52,500	57,866	52,500
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Cost of services	0	0	0	0
Gross profit	0	0	0	0
Selling, general and administrative expenses	4,351	2,690	11,338	8,249
Contingent consideration	0	0	0	0
Loss (gain) on sale of assets	0	0	0	0
Operating income (loss)	(4,351)	(2,690)	(11,338)	(8,249)
Depreciation and amortization expense	23	18	78	89
Capital expenditures	22	0	124	0
Total assets	$ 69,392	$ 87,948	$ 69,392	$ 87,948