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Stock-Based Compensation - Stock Option Activity (Details) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]    
Shares, Outstanding, Beginning Balance (in shares) 4,504,642  
Shares, Granted (in shares) 1,038,874  
Shares, Exercised (in shares) (176,616)  
Shares, Forfeited or expired (in shares) (51,423)  
Shares, Outstanding, Ending Balance (in shares) 5,315,477 4,504,642
Shares, Exercisable (in shares) 2,940,789  
Shares, Vested and expected to vest (in shares) 5,074,332  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]    
Weighted- Average Exercise Price, Outstanding, Beginning Balance (in dollars per share) $ 19.79  
Weighted- Average Exercise Price, Granted (in dollars per share) 28.49  
Weighted- Average Exercise Price, Exercised (in dollars per share) 5.03  
Weighted- Average Exercise Price, Forfeited or expired (in dollars per share) 20.90  
Weighted- Average Exercise Price, Outstanding, Ending Balance (in dollars per share) 21.97 $ 19.79
Weighted- Average Exercise Price, Exercisable (in dollars per share) 18.61  
Weighted- Average Exercise Price, Vested and expected to vest (in dollars per share) $ 21.76  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]    
Weighted- Average Remaining Contractual Term, Outstanding 7 years 4 months 24 days 7 years
Weighted- Average Remaining Contractual Term, Exercisable 6 years 1 month 6 days  
Weighted- Average Remaining Contractual Term, Vested and expected to vest 7 years 4 months 24 days  
Aggregate Intrinsic Value, Outstanding, Ending Balance $ 29,749  
Aggregate Intrinsic Value, Exercisable 25,431  
Aggregate Intrinsic Value, Vested and expected to vest $ 29,334  
Weighted-average grant-date fair value of options granted (in dollars per share) $ 18.75  
Intrinsic value of options exercised $ 3,600  
Cash received for options exercised 600  
Fair value of shares vested 3,300  
Unrecognized compensation expense related to non-vested stock-options, net of related forfeiture estimates $ 34,500  
Unrecognized compensation expense recognition period 3 years