GOODWILL AND INTANGIBLE ASSETS - Change In Carrying Amount Of Telecommunications Licenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Changes in the carrying amount of the company's telecommunications licenses, by operating segment
Balance at the beginning of the period	$ 48,291
Balance at the end of the period	95,952	$ 48,291
Telecommunications Licenses
Telecommunications licenses
Impairment of intangible assets	0	0
Changes in the carrying amount of the company's telecommunications licenses, by operating segment
Balance at the beginning of the period	48,291	43,468
Deconsolidation of subsidiary		(2,178)
Acquired licenses	47,692	7,623
Amortization		(622)
Dispositions	(31)
Balance at the end of the period	95,952	48,291
Telecommunications Licenses | U.S. Telecom
Changes in the carrying amount of the company's telecommunications licenses, by operating segment
Balance at the beginning of the period	24,944	24,944
Acquired licenses	47,692
Dispositions	(31)
Balance at the end of the period	72,605	24,944
Telecommunications Licenses | International
Changes in the carrying amount of the company's telecommunications licenses, by operating segment
Balance at the beginning of the period	23,347	18,524
Deconsolidation of subsidiary		(2,178)
Acquired licenses		7,623
Amortization		(622)
Balance at the end of the period	$ 23,347	$ 23,347