Employee Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Significant multiemployer plans
Contributions to Plan	$ 52,686	$ 44,824	$ 43,887
National Electrical Benefit Fund [Member]
Significant multiemployer plans
Contributions to Plan	6,930	6,330	6,048
National Electrical Annuity Plan [Member]
Significant multiemployer plans
Contributions to Plan	24,226	20,694	21,002
Eighth District Electrical Pension Fund [Member]
Significant multiemployer plans
Contributions to Plan	5,598	5,197	5,672
Multiemployer Plan, Individually Insignificant Multiemployer Plans [Member]
Significant multiemployer plans
Contributions to Plan	8,070	5,114	4,300
IBEW Local 1249 Pension Plan [Member]
Significant multiemployer plans
Contributions to Plan	2,042	2,103	3,147
Eighth District Electrical Pension Fund Annuity Plan [Member]
Significant multiemployer plans
Contributions to Plan	3,700	3,553	2,427
IBEW Local 769 Management Pension Plan [Member]
Significant multiemployer plans
Contributions to Plan	$ 2,120	$ 1,833	$ 1,291