Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Contract revenues:	$ 283,259	$ 269,861	$ 798,827	$ 790,497
Income from operations:	11,139	9,919	23,588	34,540
T&D [Member]
Segment Reporting Information [Line Items]
Contract revenues:	206,441	203,864	568,044	593,670
Income from operations:	14,550	13,929	40,804	47,476
C&I [Member]
Segment Reporting Information [Line Items]
Contract revenues:	76,818	65,997	230,783	196,827
Income from operations:	5,043	2,780	9,633	9,540
General Corporate [Member]
Segment Reporting Information [Line Items]
Income from operations:	$ (8,454)	$ (6,790)	$ (26,849)	$ (22,476)