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Fair Value Measurements (Schedule Of Financial Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($)
Jun. 30, 2018
Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Supplemental executive retirement plan assets $ 30,500,000 $ 30,900,000
Derivatives, net (6,500,000) 6,800,000
Total Financial Liabilities (6,500,000)  
Total Financial Assets 30,500,000 37,700,000
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Supplemental executive retirement plan assets 30,500,000 30,900,000
Derivatives, net 0 0
Total Financial Liabilities 0  
Total Financial Assets 30,500,000 30,900,000
Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Supplemental executive retirement plan assets 0 0
Derivatives, net (6,500,000) 6,800,000
Total Financial Liabilities (6,500,000)  
Total Financial Assets 0 6,800,000
Significant Unobservable Inputs (Level 3) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Supplemental executive retirement plan assets 0 0
Derivatives, net 0 0
Total Financial Liabilities 0.0  
Total Financial Assets $ 0.0 $ 0