Annual report pursuant to Section 13 and 15(d)

Stock-Based Payments - Summary of Status of Stock Options and Changes During the Period (Details)

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Stock-Based Payments - Summary of Status of Stock Options and Changes During the Period (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]    
Outstanding at beginning of year (in shares) 2,846,668  
Granted (in shares) 1,548,252  
Exercised (in shares) (214,532)  
Cancelled (in shares) (447,745)  
Outstanding at end of period (in shares) 3,732,643 2,846,668
Exercisable (in shares) 1,366,881  
Outstanding at beginning of year (in dollars per share) $ 9.25  
Granted (in dollars per share) 10.37  
Exercised (in dollars per share) 2.92  
Cancelled (in dollars per share) 10.96  
Outstanding at end of period (in dollars per share) 9.88 $ 9.25
Exercisable (in dollars per share) $ 8.34  
Remaining Contractual Life, Outstanding 7 years 10 months 25 days 8 years 2 months 12 days
Remaining Contractual Life, Exercisable 6 years 10 months 25 days  
Aggregate Intrinsic Value, Outstanding at beginning of year $ 5,713  
Aggregate Intrinsic Value, Outstanding at ending of year 1,694 $ 5,713
Aggregate Intrinsic Value, Options Exercisable $ 1,569