Operations by Business Segment (Details) $ in Thousands		3 Months Ended		6 Months Ended
		Jul. 04, 2015 USD ($)	Jun. 28, 2014 USD ($)	Jul. 04, 2015 USD ($)	Jun. 28, 2014 USD ($)	Dec. 31, 2014 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments				2
Revenues		$ 224,773	$ 213,183	$ 399,065	$ 370,570
Income (loss) from operations		27,796	23,815	23,811	19,090
Interest expense		(900)	(706)	(1,690)	(1,425)
Interest income		59	76	122	145
Other income (expense), net		(881)	(500)	(1,708)	(1,305)
Income before income taxes		26,074	22,685	20,535	16,505
Segment assets, total		408,195	366,580	408,195	366,580	$ 381,004
Utility services [Member]
Segment Reporting Information [Line Items]
Revenues		108,537	98,842	208,920	188,134
Income (loss) from operations		7,478	5,940	11,363	8,725
Segment assets, total		164,250	143,504	164,250	143,504
Residential commercial services [Member]
Segment Reporting Information [Line Items]
Revenues		115,635	113,512	189,092	181,319
Income (loss) from operations		22,712	20,134	18,823	15,897
Segment assets, total		165,587	160,201	165,587	160,201
All other [Member]
Segment Reporting Information [Line Items]
Revenues		601	829	1,053	1,117
Income (loss) from operations		(923)	(1,091)	(3,538)	(3,607)
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]	(1,471)	(1,168)	(2,837)	(1,925)
Interest expense		(900)	(706)	(1,690)	(1,425)
Interest income		59	76	122	145
Other income (expense), net		(881)	(500)	(1,708)	(1,305)
Segment assets, total	[2]	$ 78,358	$ 62,875	$ 78,358	$ 62,875

[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.