Operating Segments (Details) - USD ($)	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 240,275,000	$ 232,576,000	$ 205,677,000	$ 198,300,000	$ 206,581,000	$ 208,323,000	$ 203,662,000	$ 192,178,000	$ 876,828,000	$ 810,744,000	$ 695,993,000
Cost of Services									726,866,000	670,246,000	569,013,000
Gross Profit	40,521,000	$ 42,537,000	$ 33,840,000	$ 33,064,000	38,104,000	$ 35,398,000	$ 31,814,000	$ 35,182,000	149,962,000	140,498,000	126,980,000
Selling, General and Administrative Expense									123,920,000	120,370,000	100,558,000
Contingent consideration									103,000	(145,000)	652,000
Loss (gain) on sale of assets									(15,000)	(69,000)	810,000
Operating Income (Loss)									25,954,000	20,342,000	24,960,000
Depreciation and amortization									8,860,000	9,634,000	5,664,000
Capital Expenditures									4,563,000	4,589,000	3,417,000
Assets	421,994,000				424,494,000				421,994,000	424,494,000	394,340,000
Commercial & Industrial [Member]
Segment Reporting Information [Line Items]
Revenues									274,299,000	227,606,000	222,466,000
Cost of Services									244,656,000	208,619,000	197,679,000
Gross Profit									29,643,000	18,987,000	24,787,000
Selling, General and Administrative Expense									27,031,000	20,170,000	17,169,000
Contingent consideration									(100,000)	0	0
Loss (gain) on sale of assets									(37,000)	(32,000)	(17,000)
Operating Income (Loss)									2,749,000	(1,151,000)	7,635,000
Depreciation and amortization									2,197,000	1,648,000	1,234,000
Capital Expenditures									2,216,000	1,241,000	795,000
Assets	89,729,000				84,756,000				89,729,000	84,756,000	59,763,000
Communications [Member]
Segment Reporting Information [Line Items]
Revenues									219,655,000	225,275,000	189,635,000
Cost of Services									179,518,000	187,419,000	157,104,000
Gross Profit									40,137,000	37,856,000	32,531,000
Selling, General and Administrative Expense									26,003,000	24,219,000	20,839,000
Contingent consideration									(85,000)		0
Loss (gain) on sale of assets									(4,000)	(1,000)	0
Operating Income (Loss)									14,223,000	13,638,000	11,692,000
Depreciation and amortization									1,247,000	740,000	577,000
Capital Expenditures									647,000	2,046,000	1,102,000
Assets	80,528,000				63,917,000				80,528,000	63,917,000	68,018,000
Infrastructure Solutions [Member]
Segment Reporting Information [Line Items]
Revenues									97,163,000	83,824,000	58,003,000
Cost of Services									75,337,000	63,399,000	42,356,000
Gross Profit									21,826,000	20,425,000	15,647,000
Selling, General and Administrative Expense									18,293,000	17,859,000	12,404,000
Contingent consideration									288,000	(145,000)	652,000
Loss (gain) on sale of assets									18,000	(79,000)	826,000
Operating Income (Loss)									3,227,000	2,790,000	1,765,000
Depreciation and amortization									4,672,000	6,412,000	3,072,000
Capital Expenditures									735,000	538,000	721,000
Assets	109,506,000				106,114,000				109,506,000	106,114,000	89,447,000
Residential
Segment Reporting Information [Line Items]
Revenues									285,711,000	274,039,000	225,889,000
Cost of Services									227,355,000	210,809,000	171,874,000
Gross Profit									58,356,000	63,230,000	54,015,000
Selling, General and Administrative Expense									41,401,000	43,689,000	37,585,000
Contingent consideration											0
Loss (gain) on sale of assets									8,000	43,000	1,000
Operating Income (Loss)									16,947,000	19,498,000	16,429,000
Depreciation and amortization									637,000	565,000	509,000
Capital Expenditures									932,000	561,000	704,000
Assets	55,176,000				51,994,000				55,176,000	51,994,000	43,195,000
Corporate
Segment Reporting Information [Line Items]
Revenues									0	0	0
Cost of Services									0	0	0
Gross Profit									0	0	0
Selling, General and Administrative Expense									11,192,000	14,433,000	12,561,000
Contingent consideration											0
Loss (gain) on sale of assets									0	0	0
Operating Income (Loss)									(11,192,000)	(14,433,000)	(12,561,000)
Depreciation and amortization									107,000	269,000	272,000
Capital Expenditures									33,000	203,000	95,000
Assets	$ 87,055,000				$ 117,713,000				$ 87,055,000	$ 117,713,000	$ 133,917,000