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Retirement and Security Bonus Plans Retirement and Security Bonus Plans (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]      
401k Employer matching contributions $ 2.9 $ 2.9 $ 2.7
Employer contributions, profit sharing retirement plan 0.8 0.6 0.1
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]      
Cash Surrender Value, Fair Value Disclosure $ 2.2    
Security bonus plan      
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]      
Initial vesting percentage 25.00%    
Minimum vesting period 5 years    
Annual vesting percentage after initial period 5.00%    
Expense recognized $ 0.4 $ 0.6 $ 0.7