Summary of Significant Accounting Policies - Reconciliation of Goodwill (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Goodwill [Roll Forward] | |||
| Goodwill, beginning balance | $ 225,600 | $ 264,350 | $ 285,848 |
| Goodwill allocated to dispositions of a business | 0 | (10,010) | (21,498) |
| Goodwill, ending balance | 225,600 | 225,600 | $ 264,350 |
| Continuing operations and discontinued operations | |||
| Goodwill [Roll Forward] | |||
| Goodwill, beginning balance | 254,340 | ||
| Goodwill, ending balance | $ 254,340 | $ 254,340 | |