Stock-Based Compensation - Assumptions Used For Stock Options (Details) - Stock option awards - $ / shares |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Weighted average grant date fair value per share (in dollars per share) | $ 7.96 | $ 7.21 |
| Expected term (in years) | 6 years | 6 years |
| Expected stock volatility | 37.00% | 38.20% |
| Dividend yield | 0.00% | 0.00% |
| Risk-free interest rate | 2.30% | 2.00% |