Intangible Assets and Goodwill (Goodwill) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Goodwill [Roll Forward]
Balance at January 1, 2018	$ 25,569
Acquisitions	924,629
Balance at March 31, 2018	950,198
GCI Holdings
Goodwill [Roll Forward]
Balance at January 1, 2018	0
Acquisitions	924,629
Balance at March 31, 2018	924,629
Corporate and other
Goodwill [Roll Forward]
Balance at January 1, 2018	25,569
Acquisitions	0
Balance at March 31, 2018	$ 25,569