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Fair Value Measurements - Estimated Fair Value and Carrying Value of Long-term Debt (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Oct. 01, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Carrying Value $ 0 $ 37,502  
Secured Notes | Building Note      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair Value     $ 36,600
Carrying Value 0 37,502  
Level 2 | Secured Notes | Building Note      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair Value $ 0 $ 42,526