Operations by Business Segment (Details) $ in Thousands		3 Months Ended		9 Months Ended
		Oct. 03, 2015 USD ($)	Sep. 27, 2014 USD ($)	Oct. 03, 2015 USD ($)	Sep. 27, 2014 USD ($)	Dec. 31, 2014 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments				2
Revenues		$ 224,981	$ 216,604	$ 624,046	$ 587,174
Income (loss) from operations		16,177	17,144	39,988	36,234
Interest expense		(827)	(676)	(2,517)	(2,101)
Interest income		85	56	207	201
Other income (expense), net		(2,068)	(1,112)	(3,776)	(2,417)
Income before income taxes		13,367	15,412	33,902	31,917
Segment assets, total		413,116	386,596	413,116	386,596	$ 381,004
Utility services [Member]
Segment Reporting Information [Line Items]
Revenues		114,884	108,096	323,804	296,230
Income (loss) from operations		6,267	5,725	17,630	14,450
Segment assets, total		164,841	155,231	164,841	155,231
Residential commercial services [Member]
Segment Reporting Information [Line Items]
Revenues		109,108	107,671	298,200	288,990
Income (loss) from operations		13,513	13,421	32,336	29,318
Segment assets, total		163,935	156,685	163,935	156,685
All other [Member]
Segment Reporting Information [Line Items]
Revenues		989	837	2,042	1,954
Income (loss) from operations		(1,378)	(514)	(4,916)	(4,121)
Segment assets, total		0	0	0	0
Reconciling adjustments [Member]
Segment Reporting Information [Line Items]
Revenues		0	0	0	0
Income (loss) from operations	[1]	(2,225)	(1,488)	(5,062)	(3,413)
Interest expense		(827)	(676)	(2,517)	(2,101)
Interest income		85	56	207	201
Other income (expense), net		(2,068)	(1,112)	(3,776)	(2,417)
Segment assets, total	[2]	$ 84,340	$ 74,680	$ 84,340	$ 74,680

[1] (a)Reclassification of depreciation expense and allocation of corporate expenses.

[2] (b)Corporate assets include cash, prepaid expenses, corporate facilities, enterprise-wide information systems and other nonoperating assets.