Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Intangible Assets And Goodwill [Line Items]
Goodwill gross carrying amount	$ 46,994	$ 46,781
Goodwill accumulated amortization	0	0
Goodwill net carrying amount	46,994	46,781
Accumulated Amortization	5,183	4,684
Amortizable intangible assets net carrying amount	1,778
Intangible Assets, Gross (Excluding Goodwill)	16,035	16,250
Intangible Assets, Net (Excluding Goodwill)	10,852	11,566
T&D [Member]
Schedule Of Intangible Assets And Goodwill [Line Items]
Goodwill gross carrying amount	40,224	40,224
Goodwill accumulated amortization	0	0
Goodwill net carrying amount	40,224	40,224
C&I [Member]
Schedule Of Intangible Assets And Goodwill [Line Items]
Goodwill gross carrying amount	6,770	6,557
Goodwill accumulated amortization	0	0
Goodwill net carrying amount	6,770	6,557
Backlog [Member]
Schedule Of Intangible Assets And Goodwill [Line Items]
Amortizable intangible assets gross carrying amount	989	989
Accumulated Amortization	989	989
Amortizable intangible assets net carrying amount	0	0
Customer Relationships [Member]
Schedule Of Intangible Assets And Goodwill [Line Items]
Amortizable intangible assets gross carrying amount	5,277	5,266
Accumulated Amortization	4,069	3,590
Amortizable intangible assets net carrying amount	1,208	1,676
Trade Names [Member]
Schedule Of Intangible Assets And Goodwill [Line Items]
Amortizable intangible assets gross carrying amount	695	695
Accumulated Amortization	125	79
Amortizable intangible assets net carrying amount	570	616
Indefinite-lived Intangible Assets	9,074	8,556
Intangible Assets, Gross (Excluding Goodwill)	0	0
Intangible Assets, Net (Excluding Goodwill)	9,074	8,556
Unallocated Intangible Assets [Member]
Schedule Of Intangible Assets And Goodwill [Line Items]
Amortizable intangible assets gross carrying amount	0	744
Accumulated Amortization	0	26
Amortizable intangible assets net carrying amount	$ 0	$ 718