Intangible Assets and Goodwill (Goodwill) (Details) $ in Thousands  | 
9 Months Ended | 
|---|---|
| 
 Sep. 30, 2018  
USD ($) 
 | |
| Goodwill [Roll Forward] | |
| Balance at January 1, 2018 | $ 25,569 | 
| Acquisitions | 942,118 | 
| Balance at September 30, 2018 | 967,687 | 
| GCI Holdings | |
| Goodwill [Roll Forward] | |
| Balance at January 1, 2018 | 0 | 
| Acquisitions | 942,118 | 
| Balance at September 30, 2018 | 942,118 | 
| Corporate and other | |
| Goodwill [Roll Forward] | |
| Balance at January 1, 2018 | 25,569 | 
| Acquisitions | 0 | 
| Balance at September 30, 2018 | $ 25,569 | 
| X | ||||||||||
- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
  | 
| X | ||||||||||
- Definition Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
  | 
| X | ||||||||||
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. No definition available. 
  | 
| X | ||||||||||
- Details 
  | 
| X | ||||||||||
- Details 
  |