Internal-Use Software Development Costs - Capitalized Computer Software Future Amortization Expense (Details) - USD ($) $ in Thousands |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Research and Development [Abstract] | ||
| 2018 | $ 7,492 | |
| 2019 | 7,075 | |
| 2020 | 3,233 | |
| 2021 | 264 | |
| Internal use software development costs, net | $ 18,064 | $ 17,609 |