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Stock-Based Compensation - Summary of Restricted Stock and Restricted Stock Unit Activity (Details) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Restricted Stock [Member]      
Number of Restricted Stock Awards      
Unvested, Beginning Balance (shares) 1,562,918 2,152,157 2,173,982
Granted (shares) 1,092,534 927,306 1,203,675
Share issuance upon approved achievement date (shares) (635,320) (1,137,555) (889,857)
Forfeited (shares) (218,002) (378,990) (335,643)
Unvested, Ending Balance (shares) 1,802,130 1,562,918 2,152,157
Weighted Average Fair Value per Share at Grant Date      
Beginning Balance ($ per share) $ 6.27 $ 6.29 $ 6.58
Granted ($ per share) 17.35 6.22 5.93
Share issuance upon approved achievement date ($ per share) 6.51 6.38 6.49
Forfeited ($ per share) 7.56 5.95 6.33
Ending Balance ($ per share) $ 12.75 $ 6.27 $ 6.29
Restricted Stock Units (RSUs) [Member]      
Number of Restricted Stock Awards      
Unvested, Beginning Balance (shares) 217,206 0  
Granted (shares) 138,334 217,206  
Market-based achievement adjustment at vesting (shares) 100,326    
Share issuance upon approved achievement date (shares) (200,652)    
Unvested, Ending Balance (shares) 255,214 217,206 0
Weighted Average Fair Value per Share at Grant Date      
Beginning Balance ($ per share) $ 6.49 $ 0.00  
Granted ($ per share) 28.31 6.49  
Market-based achievement adjustment at vesting ($ per share) 6.49    
Share issuance upon approved achievement date ($ per share) 6.49    
Ending Balance ($ per share) $ 17.91 $ 6.49 $ 0.00