Summary of Significant Accounting Policies - TPG Investment in Company (Details) - TPG Management - USD ($) $ in Millions |
12 Months Ended | |||
|---|---|---|---|---|
Jun. 19, 2013 |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| TPG Investment in Company | ||||
| Ownership percentage (percent) | 43.70% | |||
| Management Services Agreement | ||||
| TPG Investment in Company | ||||
| Monitoring fee (up to) | $ 0.5 | |||
| TPG ownership percentage (at least) | 30.00% | |||
| Payments for Fees | $ 0.4 | $ 0.4 | $ 0.4 | |