Operations by Business Segment and Geographic Information Operations by Busines Segment (Details) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2018 USD ($)	Sep. 29, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jul. 01, 2017 USD ($)	Apr. 01, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments										2
Revenues										$ 1,024,791	$ 915,958	$ 845,678
Income (loss) from operations		$ 16,971	$ 14,585	$ 29,800	$ (5,666)	$ 11,478	$ 19,049	$ 25,659	$ (3,995)	55,690	52,191	48,867
Interest expense										7,039	4,886	4,393
Interest income										350	292	255
Other										(11,505)	(9,603)	(7,485)
Income before income taxes										37,496	37,994	37,244
Depreciation										54,914	50,702	47,284
Amortization										2,055	2,384	2,306
Capital expenditures										60,410	57,100	56,646
Segment assets, total		526,623				473,135				526,623	473,135	423,939
Utility Services
Segment Reporting Information [Line Items]
Revenues										537,484	466,727	433,379
Income (loss) from operations										32,370	18,223	19,256
Depreciation										29,526	27,928	26,855
Amortization										211	122	135
Capital expenditures										32,148	26,910	28,660
Segment assets, total		239,426				189,662				239,426	189,662	171,220
Residential Commercial Services
Segment Reporting Information [Line Items]
Revenues										486,005	446,028	410,878
Income (loss) from operations										47,812	41,158	36,640
Depreciation										21,720	19,384	17,198
Amortization										1,842	2,240	2,136
Capital expenditures										22,256	23,199	21,819
Segment assets, total		208,369				197,698				208,369	197,698	166,858
All Other
Segment Reporting Information [Line Items]
Revenues										1,302	3,203	1,421
Income (loss) from operations										(19,816)	(2,634)	(4,318)
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	[1]									(4,676)	(4,556)	(2,711)
Interest expense										7,039	4,886	4,393
Interest income										350	292	255
Other										(11,505)	(9,603)	(7,485)
Depreciation	[2]									3,668	3,390	3,231
Amortization										2	22	35
Capital expenditures										6,006	6,991	6,167
Segment assets, total	[3]	$ 78,828				$ 85,775				$ 78,828	$ 85,775	$ 85,861

[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.