Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements and Derivative Instruments (Assets and liabilities measured at fair value on a recurring basis) (Details)

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Fair Value Measurements and Derivative Instruments (Assets and liabilities measured at fair value on a recurring basis) (Details) - Fair Value, Measurements, Recurring [Member] - USD ($)
$ in Thousands
Jun. 30, 2016
Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Deferred compensation plan assets (mutual funds) $ 1,486 $ 1,728
Derivative stock appreciation rights 21,780 32,820
Fair Value, Inputs, Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Deferred compensation plan assets (mutual funds) 1,486 1,728
Derivative stock appreciation rights 0 0
Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Deferred compensation plan assets (mutual funds) 0 0
Derivative stock appreciation rights 0 0
Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Deferred compensation plan assets (mutual funds) 0 0
Derivative stock appreciation rights $ 21,780 $ 32,820