Operations by Business Segment (Details) $ in Thousands		3 Months Ended
		Mar. 28, 2020 USD ($)	Mar. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments		2
Revenues		$ 288,280	$ 247,889
Income (loss) from operations		3,934	2,966
Interest expense		(1,946)	(2,151)
Interest income		101	83
Other income (expense), net		(1,899)	(1,655)
Income before income taxes		190	(757)
Segment assets, total		675,150	565,478	$ 596,862
Utility [Member]
Segment Reporting Information [Line Items]
Revenues		185,749	140,469
Income (loss) from operations		15,632	5,880
Segment assets, total		291,426	231,060
Residential commercial [Member]
Segment Reporting Information [Line Items]
Revenues		101,953	107,395
Income (loss) from operations		(5,661)	507
Segment assets, total		221,956	217,044
All other [Member]
Segment Reporting Information [Line Items]
Revenues		578	25
Income (loss) from operations		(4,695)	(2,968)
Segment assets, total		0	0
Reconciling adjustments [Member]
Segment Reporting Information [Line Items]
Revenues		0	0
Income (loss) from operations	[1]	(1,342)	(453)
Interest expense		(1,946)	(2,151)
Interest income		101	83
Other income (expense), net		(1,899)	(1,655)
Segment assets, total	[2]	$ 161,768	$ 117,374

[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.