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Fair Value Measurements - Estimated Fair Value and Carrying Value of Long-Term Debt (Details) - Secured Notes - New Building Note - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Oct. 04, 2016
Fair Value, Assets and Liabilities Measured on Recurring Basis      
Fair Value     $ 36,600
Carrying value $ 0 $ 37,502  
Fair Value Measurements Level 2      
Fair Value, Assets and Liabilities Measured on Recurring Basis      
Fair Value $ 0 $ 42,526