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Stock-Based Compensation - Stock-based compensation (Details) - shares
12 Months Ended 120 Months Ended
Dec. 31, 2018
Apr. 07, 2017
Jan. 29, 2018
2007 LTIP      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted (in shares)   0  
Common stock reserved for issuance   11,500,000  
2018 LTIP      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock reserved for issuance     3,300,000
Stock options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Minimum period for non-cash exchange of previously issued shares in exchange for newly issued shares 6 months