Operations by Business Segment (Details) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 27, 2020 USD ($)	Jun. 29, 2019 USD ($)	Jun. 27, 2020 USD ($)	Jun. 29, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments				2
Revenues		$ 319,247	$ 301,434	$ 607,527	$ 549,323
Income (loss) from operations		44,311	30,282	48,245	33,248
Interest expense		(1,952)	(2,428)	(3,898)	(4,579)
Interest income		96	93	197	176
Other income (expense), net		(1,152)	(3,153)	(3,051)	(4,808)
Income before income taxes		41,303	24,794	41,493	24,037
Segment assets, total		658,011	570,149	658,011	570,149	$ 596,862
Utility [Member]
Segment Reporting Information [Line Items]
Revenues		176,735	151,192	362,484	291,661
Income (loss) from operations		20,884	9,995	36,516	15,875
Segment assets, total		301,477	235,687	301,477	235,687
Residential commercial [Member]
Segment Reporting Information [Line Items]
Revenues		142,905	149,970	244,858	257,365
Income (loss) from operations		27,630	26,598	21,969	27,105
Segment assets, total		231,985	233,220	231,985	233,220
All other [Member]
Segment Reporting Information [Line Items]
Revenues		(393)	272	185	297
Income (loss) from operations		(3,552)	(5,401)	(8,247)	(8,369)
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]	(651)	(910)	(1,993)	(1,363)
Interest expense		(1,952)	(2,428)	(3,898)	(4,579)
Interest income		96	93	197	176
Other income (expense), net		(1,152)	(3,153)	(3,051)	(4,808)
Segment assets, total	[2]	$ 124,549	$ 101,242	$ 124,549	$ 101,242

[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.