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Stock-Based Compensation - Performance Stock Unit Activity (Details) - Performance stock units - $ / shares
9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Awards    
Outstanding, beginning of period (in shares) 386,459  
Granted (in shares) 486,213  
Vested (in shares) 0  
Forfeited (in shares) 0  
Outstanding, end of period (in shares) 872,672  
Weighted Average Grant Date Fair Value    
Beginning of period (in dollars per share) $ 21.94  
Granted (in dollars per share) 6.68 $ 22.35
Vested (in dollars per share) 0  
Forfeited (in dollar per share) 0  
End of period (in dollars per share) $ 13.44