Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Schedule of Fair Value of Assets and Liabilities Measured on Recurring Basis (Details)

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Fair Value Measurements - Schedule of Fair Value of Assets and Liabilities Measured on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Fair Value, Inputs, Level 1    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Construction reserve funds $ 28,109 $ 28,221
Fair Value, Inputs, Level 2    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Derivative Liability 2,295 1,659
Fair Value, Inputs, Level 3    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Conversion Option Liability on Convertible Senior Notes $ 6,201 $ 5,276