Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements and Derivative Instrument (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details)

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Fair Value Measurements and Derivative Instrument (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - Fair Value, Measurements, Recurring [Member] - USD ($)
$ in Thousands
Jun. 30, 2017
Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Deferred compensation plan assets (mutual funds) $ 1,354 $ 1,477
Derivative stock appreciation rights 71,400 29,700
Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Deferred compensation plan assets (mutual funds) 1,354 1,477
Derivative stock appreciation rights 0 0
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
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 $ 71,400 $ 29,700