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Stock-Based Compensation - Non-vested Restricted Stock Unit Awards (Details) - Restricted stock unit awards - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Restricted Stock Unit (RSU) Awards Outstanding      
Aggregate grant date fair value of restricted stock unit awards outstanding $ 11,398 $ 7,050 $ 5,515
Unrecognized compensation cost related to non-vested restricted stock unit awards $ 5,891    
Weighted-average period over which unrecognized compensation cost is expected to be recognized 2 years 5 months 26 days    
Number of Restricted Stock Awards Outstanding      
Non-vested restricted stock unit awards outstanding, beginning balance (shares) 2,350,054    
Restricted stock unit awards granted (shares) 1,364,236    
Restricted stock unit awards forfeited (shares) (265,681)    
Restricted stock unit awards vested (shares) (973,568)    
Non-vested restricted stock unit awards outstanding, ending balance (shares) 2,475,041 2,350,054  
Weighted Average Grant Date Fair Value Per Share      
Non-vested restricted stock unit awards outstanding, beginning of year (usd per shares) $ 3.00    
Restricted stock unit awards granted (usd per shares) 6.10    
Restricted stock unit awards forfeited (usd per shares) 4.32    
Restricted stock unit awards vested (usd per shares) 2.91    
Non-vested restricted stock unit awards outstanding, end of year (usd per shares) $ 4.61 $ 3.00  
Maximum      
Restricted Stock Unit (RSU) Awards Outstanding      
Vesting period (years) 4 years