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Stock-Based Compensation (Schedule of Weighted-average Fair Value Assumptions) (Details) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted-average fair value (in usd per share) $ 0.00 $ 0.00 $ 7.80
Expected volatility 0.00% 0.00% 60.00%
Risk-free interest rate 0.00% 0.00%  
Expected dividend yield 0.00% 0.00% 0.00%
Derived term in years 0 years 0 years  
Stock Options | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate     0.76%
Derived term in years     3 years
Stock Options | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate     1.46%
Derived term in years     4 years