Operations by Business Segment and Geographic Information Operations by Busines Segment (Details) $ in Thousands		3 Months Ended									12 Months Ended
		Dec. 31, 2016 USD ($)		Oct. 01, 2016 USD ($)	Jul. 02, 2016 USD ($)	Apr. 02, 2016 USD ($)	Dec. 31, 2015 USD ($)	Oct. 03, 2015 USD ($)	Jul. 04, 2015 USD ($)	Apr. 04, 2015 USD ($)	Dec. 31, 2016 USD ($)		Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Segment reporting information [Line Items]
Number of reportable segments											2
Revenues											$ 845,678		$ 821,904	$ 789,911
Income (loss) from operations		$ 11,163		$ 15,042	$ 24,286	$ (5,120)	$ 4,120	$ 16,177	$ 27,796	$ (3,985)	45,371		44,108	44,003
Interest expense											4,393		3,355	2,948
Interest income											255		249	295
Other											(3,989)		(5,744)	(3,050)
Income before income taxes											37,244		35,258	38,300
Depreciation											47,284		44,677	40,970
Amortization											2,306		2,214	2,070
Capital expenditures											56,646		56,047	55,731
Segment assets, total		423,939					393,586				423,939		393,586	381,004
Utility Services
Segment reporting information [Line Items]
Revenues											433,379		433,117	404,519
Income (loss) from operations											19,256		24,273	21,382
Depreciation											26,855		25,466	23,225
Amortization											135		144	174
Capital expenditures											28,660		26,853	25,994
Segment assets, total		171,220					145,306				171,220		145,306	150,002
Residential Commercial Services
Segment reporting information [Line Items]
Revenues											410,878		386,327	386,274
Income (loss) from operations											36,640		35,271	37,232
Depreciation											17,198		15,592	14,544
Amortization											2,136		2,062	1,896
Capital expenditures											21,819		22,853	17,490
Segment assets, total		166,858					162,679				166,858		162,679	144,413
All Other
Segment reporting information [Line Items]
Revenues											1,421		2,460	(882)
Income (loss) from operations											(4,318)		(5,368)	(6,037)
Depreciation											0		0	0
Amortization											0		0	0
Capital expenditures											0		0	0
Segment assets, total		0					0				0		0	0
Corporate, Non-Segment [Member]
Segment reporting information [Line Items]
Revenues											0		0	0
Income (loss) from operations											(6,207)	[1]	(10,068)	(8,574)	[1]
Interest expense											4,393		3,355	2,948
Interest income											255		249	295
Other											(3,989)		(5,744)	(3,050)
Depreciation	[2]										3,231		3,619	3,201
Amortization											35		8	0
Capital expenditures											6,167		6,341	12,247
Segment assets, total		$ 85,861	[3]				$ 85,601				$ 85,861	[3]	$ 85,601	$ 86,589	[3]

[1] Reconciling adjustments from segment reporting to consolidated external financial reporting include reclassification of depreciation expense and allocation of corporate expenses.

[2] Adjustments to declining-balance method depreciation expense from straight-line method and depreciation and amortization of corporate assets.

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