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Employee Retirement Plans (Details 6) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Multiemployer Plans [Line Items]      
PPA Zone Status Yellow Yellow  
Financial improvement plan status Implemented    
Multiemployer plan contributions $ 2.3 $ 2.5 $ 0.6
Surcharge imposed No    
Expiration date of collective bargaining agreement Jul. 03, 2019    
Boilermaker-Blacksmith National Pension Trust      
Multiemployer Plans [Line Items]      
Employer Identification Number 486168020