Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues	$ 205,677	$ 203,662	$ 403,977	$ 395,840
Cost of services	171,837	171,848	337,073	328,844
Gross profit	33,840	31,814	66,904	66,996
Selling, general and administrative expenses	29,647	30,120	59,736	58,314
Contingent consideration expense	71	83	71	83
Loss (gain) on sale of assets	(20)	(6)	(34)	(13)
Operating income (loss)	4,142	1,617	7,131	8,612
Depreciation and amortization	2,061	2,319	4,269	4,378
Capital expenditures	1,124	1,095	2,327	2,891
Assets	384,987	407,974	384,987	407,974	$ 424,494
Commercial & Industrial [Member]
Segment Reporting Information [Line Items]
Revenues	65,589	55,272	118,591	109,228
Cost of services	59,068	52,604	107,227	100,454
Gross profit	6,521	2,668	11,364	8,774
Selling, general and administrative expenses	6,849	5,261	12,644	9,585
Loss (gain) on sale of assets	(17)	(8)	(29)	(7)
Operating income (loss)	(311)	(2,585)	(1,251)	(804)
Depreciation and amortization	527	171	1,084	654
Capital expenditures	413	481	923	644
Assets	72,559	54,485	72,559	54,485
Communications [Member]
Segment Reporting Information [Line Items]
Revenues	50,244	61,674	104,703	114,977
Cost of services	40,892	52,378	86,231	97,710
Gross profit	9,352	9,296	18,472	17,267
Selling, general and administrative expenses	6,201	6,120	12,285	11,834
Loss (gain) on sale of assets	(8)	(1)	(9)	(1)
Operating income (loss)	3,159	3,177	6,196	5,434
Depreciation and amortization	219	171	435	345
Capital expenditures	398	481	473	1,560
Assets	60,102	68,475	60,102	68,475
Infrastructure Solutions [Member]
Segment Reporting Information [Line Items]
Revenues	23,866	18,793	45,551	37,270
Cost of services	18,842	14,515	35,842	27,617
Gross profit	5,024	4,278	9,709	9,653
Selling, general and administrative expenses	4,637	4,222	9,194	8,322
Contingent consideration expense	71	83	71	83
Loss (gain) on sale of assets	6	6	5	(2)
Operating income (loss)	310	(33)	439	1,250
Depreciation and amortization	1,140	1,622	2,383	2,945
Capital expenditures	205	56	345	137
Assets	100,884	107,535	100,884	107,535
Residential [Member]
Segment Reporting Information [Line Items]
Revenues	65,978	67,923	135,132	134,365
Cost of services	53,035	52,351	107,773	103,063
Gross profit	12,943	15,572	27,359	31,302
Selling, general and administrative expenses	9,688	10,932	20,054	21,485
Loss (gain) on sale of assets	(1)	(3)	(1)	(3)
Operating income (loss)	3,256	4,643	7,306	9,820
Depreciation and amortization	155	151	296	301
Capital expenditures	108	108	586	347
Assets	47,695	50,743	47,695	50,743
Corporate [Member]
Segment Reporting Information [Line Items]
Revenues	0	0
Cost of services	0	0
Gross profit	0	0
Selling, general and administrative expenses	2,272	3,585	5,559	7,088
Loss (gain) on sale of assets	0	0
Operating income (loss)	(2,272)	(3,585)	(5,559)	(7,088)
Depreciation and amortization	20	69	71	133
Capital expenditures	0	15		203
Assets	$ 103,747	$ 126,736	$ 103,747	$ 126,736