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Commitments and Contingencies - Schedule of Minimum Principal Payments Due on Long-term Debt (Details) - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]    
Mandatory prepayment pursuant to excess cash flow $ 4,200  
2019   $ 2,187
2020   4,375
2021   4,375
2022   4,375
2023   146,788
Thereafter   $ 0