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Employee Benefit Plans (Summary Of Current Allocation Percentages Of Plan Assets) (Details)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Horizon Defined Benefit Plan    
Defined Benefit Plan Disclosure [Line Items]    
Target Allocation 100.00%  
Percentage of Plan Assets 100.00% 100.00%
Horizon Defined Benefit Plan | Common stocks    
Defined Benefit Plan Disclosure [Line Items]    
Target Allocation 62.50%  
Allowable-Allocation Range, Minimum 35.00%  
Allowable-Allocation Range, Maximum 88.00%  
Percentage of Plan Assets 48.00% 51.00%
Horizon Defined Benefit Plan | Debt Securities    
Defined Benefit Plan Disclosure [Line Items]    
Target Allocation 15.00%  
Allowable-Allocation Range, Minimum 10.00%  
Allowable-Allocation Range, Maximum 40.00%  
Percentage of Plan Assets 25.00% 20.00%
Horizon Defined Benefit Plan | Cash and Cash Equivalents    
Defined Benefit Plan Disclosure [Line Items]    
Target Allocation 2.50%  
Allowable-Allocation Range, Minimum 2.00%  
Allowable-Allocation Range, Maximum 20.00%  
Percentage of Plan Assets 15.00% 10.00%
Horizon Defined Benefit Plan | Alternative investments    
Defined Benefit Plan Disclosure [Line Items]    
Target Allocation 20.00%  
Allowable-Allocation Range, Minimum 0.00%  
Allowable-Allocation Range, Maximum 25.00%  
Percentage of Plan Assets 12.00% 19.00%
Community Defined Benefit Plan    
Defined Benefit Plan Disclosure [Line Items]    
Target Allocation 100.00%  
Percentage of Plan Assets 100.00% 100.00%
Community Defined Benefit Plan | Common stocks    
Defined Benefit Plan Disclosure [Line Items]    
Target Allocation 40.00%  
Allowable-Allocation Range, Minimum 29.00%  
Allowable-Allocation Range, Maximum 51.00%  
Percentage of Plan Assets 41.00% 25.00%
Community Defined Benefit Plan | Debt Securities    
Defined Benefit Plan Disclosure [Line Items]    
Target Allocation 60.00%  
Allowable-Allocation Range, Minimum 42.00%  
Allowable-Allocation Range, Maximum 81.00%  
Percentage of Plan Assets 59.00% 75.00%