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Fair Value Measurement - Financial Assets and Liabilities (Details)
$ in Thousands
6 Months Ended
Jun. 30, 2020
USD ($)
item
Dec. 31, 2019
USD ($)
Fair value of financial instruments    
Transfer of asset levels within the fair value hierarchy $ 0  
Minimum number of investment funds in rabbi trust for deferred compensation plan | item 1  
Fair value measured on a recurring basis | Level 1    
Fair value of financial instruments    
Deferred compensation plan - assets $ 45,542 $ 44,623
Deferred compensation plan - liabilities $ (45,473) $ (44,679)