Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Financial Assets and Liabilities (Details)

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Fair Value Measurements - Financial Assets and Liabilities (Details) - Fair Value, Measurements, Recurring - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Level 1 | Other assets    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Non-COLI assets held in Deferred Supplemental Compensation Plan $ 409 $ 389
Level 2 | Other current assets    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Interest rate swap agreements $ 689 $ 294