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Stock-Based Compensation - Restricted Stock Unit Activity (Details) - Restricted stock units
shares in Thousands
3 Months Ended
Mar. 31, 2019
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]  
Outstanding at beginning of period (in shares) | shares 289
Granted (in shares) | shares 167
Vested (in shares) | shares (31)
Canceled (in shares) | shares (7)
Outstanding at end of period (in shares) | shares 418
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]  
Nonvested at beginning of period - Weighted average fair value per share at grant date (in usd per share) | $ / shares $ 25.56
Granted - Weighted average fair value per share at grant date (in usd per share) | $ / shares 52.66
Vested - Weighted average fair value per share at grant date (in usd per share) | $ / shares 42.65
Canceled - Weighted average fair value per share at grant date (in usd per share) | $ / shares 18.81
Nonvested at end of period - Weighted average fair value per share at grant date (in usd per share) | $ / shares $ 35.27