Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Contract revenues:	$ 271,184	$ 269,861	$ 276,488	$ 244,148	$ 250,979	$ 248,473	$ 228,877	$ 215,638	$ 1,061,681	$ 943,967	$ 902,729
Income from operations:									44,841	58,404	55,617
T&D [Member]
Segment Reporting Information [Line Items]
Contract revenues:									794,898	699,595	722,387
Income from operations:									63,155	75,439	81,413
C&I [Member]
Segment Reporting Information [Line Items]
Contract revenues:									266,783	244,372	180,342
Income from operations:									13,592	16,542	10,423
General Corporate [Member]
Segment Reporting Information [Line Items]
Income from operations:									$ (31,906)	$ (33,577)	$ (36,219)