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Nature of Business and Liquidity - Liquidity (Additional Information) (Details) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended
Jul. 31, 2018
Nov. 12, 2019
Sep. 30, 2019
Dec. 31, 2018
Subsidiary, Sale of Stock [Line Items]        
Long-term Debt     $ 663,969 $ 741,281
IPO        
Subsidiary, Sale of Stock [Line Items]        
Offering price per share (in dollars per share) $ 15.00      
Net proceeds from stock offering $ 282,300      
Subsequent Event | Convertible Promissory Notes due December 2020, Recourse | Convertible promissory notes        
Subsidiary, Sale of Stock [Line Items]        
Long-term Debt   $ 312,300