Basis of Presentation, Summary of Significant Accounting Policies and Change in Accounting Principle - Intangible Assets, Net (Details) |
12 Months Ended |
|---|---|
Dec. 31, 2018 | |
| Corporate trade name | Minimum | |
| Finite-Lived Intangible Assets [Line Items] | |
| Useful life | 10 years |
| Corporate trade name | Maximum | |
| Finite-Lived Intangible Assets [Line Items] | |
| Useful life | 20 years |
| Customer relationships | Minimum | |
| Finite-Lived Intangible Assets [Line Items] | |
| Useful life | 15 years |
| Customer relationships | Maximum | |
| Finite-Lived Intangible Assets [Line Items] | |
| Useful life | 25 years |
| Technology | |
| Finite-Lived Intangible Assets [Line Items] | |
| Useful life | 5 years |
| Provider network contracts | |
| Finite-Lived Intangible Assets [Line Items] | |
| Useful life | 5 years |