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Textuals (Details) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Schedule of Employee Benefit Plans [Line Items]        
Defined Benefit Plan, Pension, Vested Percentage   100.00%    
Defined contribution plan, employer discretionary contribution amount       $ 9,700,000
Defined contribution plan, cost recognized   $ 18,500,000 $ 18,100,000 $ 28,300,000
Deferred Compensation Liability, Classified, Noncurrent   21,700,000 23,500,000  
Defined Benefit Plan, Contributions by Plan Participants   $ 709,000 $ 735,000  
United States        
Schedule of Employee Benefit Plans [Line Items]        
Defined contribution plan, employer matching contribution, percent   50.00%    
Defined contribution plan, maximum annual contribution per employee, percent   6.00%    
Canada        
Schedule of Employee Benefit Plans [Line Items]        
Defined Benefit Plan, Contributions by Plan Participants   $ 0.02    
Canada | Minimum        
Schedule of Employee Benefit Plans [Line Items]        
Defined contribution plan, employer matching contribution, percent   3.00%    
Canada | Maximum        
Schedule of Employee Benefit Plans [Line Items]        
Defined contribution plan, employer matching contribution, percent   5.00%    
Canada | Supplemental Employee Retirement Plan [Member]        
Schedule of Employee Benefit Plans [Line Items]        
Defined Benefit Plan, Pension, Vested Percentage   100.00%    
Defined Benefit Plan, Contributions by Plan Participants   $ 0.04    
Scenario, Forecast [Member]        
Schedule of Employee Benefit Plans [Line Items]        
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year $ 400,000