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Pension PLANS: (Details) - USD ($)
$ in Thousands
9 Months Ended 12 Months Ended
Sep. 30, 2015
Sep. 27, 2014
Dec. 31, 2013
Dec. 31, 2014
Dec. 31, 2012
Dec. 31, 2011
Actuarially Determined Valuation Technique [Member] | Scenario, Adjustment [Member]            
Pension plans            
Percentage of funded status     65.11%   66.41% 66.86%
Multi-employer defined benefit pension plan            
Pension Plans            
Percentage of annual compounded surcharge for rehabilitation within ten years 5.00%          
Percentage of interim surcharge 5.00%          
Projection period beyond which plan is projected to emerge from critical status, under the Rehabilitant Plan 30 years          
Rehabilitation period 10 years          
Estimated liability upon withdrawal from plan       $ 56,400 $ 37,200  
Pension plans            
Pension expense $ 2,013 $ 2,028        
Increase in surcharge $ 349 $ 268        
Multi-employer defined benefit pension plan | Market Approach Valuation Technique [Member] | Scenario, Adjustment [Member]            
Pension plans            
Percentage of funded status     60.20%   55.30%  
Multi-employer defined benefit pension plan | Active participants | Scenario, Adjustment [Member]            
Pension plans            
Percentage of participants     20.80%      
Multi-employer defined benefit pension plan | Retired or separated from service and receiving benefits | Scenario, Adjustment [Member]            
Pension plans            
Percentage of participants     51.40%      
Multi-employer defined benefit pension plan | Retired or separated from service and entitled to receive future benefits | Scenario, Adjustment [Member]            
Pension plans            
Percentage of participants     27.80%