Stock-Based Compensation - Valuation Assumptions (Details) - USD ($) $ / shares in Units, $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Options granted (shares) | 0 | 132,000 |
| Options granted, weighted average exercise price (usd per share) | $ 0.00 | $ 23.80 |
| Weighted average grant-date fair value per share (usd per share) | $ 9.29 | |
| Stock Options and PSOs | ||
| Weighted average Black-Scholes model assumptions: | ||
| Risk-free interest rate | 2.04% | |
| Expected term (in years) | 6 years 4 months 24 days | |
| Expected volatility | 35.00% | |
| Expected dividend yield | 0.00% | |
| Remaining stock-based compensation expense for unvested options, not yet recognized | $ 1.5 | |
| Stock-based compensation expense, weighted average recognition period | 1 year 5 months 1 day | |