SEGMENT REPORTING (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Segment reporting
Number of reportable segments | segment									3
Revenue
Revenue	$ 107,701	$ 122,132	$ 123,245	$ 128,115	$ 128,531	$ 138,795	$ 99,991	$ 89,686	$ 481,193	$ 457,003	$ 355,369
Depreciation and amortization									86,934	75,980	56,890
Non-cash stock-based compensation									6,977	6,410	4,975
Operating income (loss)	41,357	$ (19,525)	$ 15,843	$ 17,793	9,911	$ 22,081	$ 1,912	$ 15,893	55,468	49,797	78,595
Segment Assets
Cash, Cash equivalents, and Investments	215,032				278,958				215,032	278,958
Total current assets	342,928				367,369				342,928	367,369
Fixed assets, net	643,146				647,712				643,146	647,712
Goodwill	63,970				62,873				63,970	62,873	45,077
Total assets	1,205,605				1,198,218				1,205,605	1,198,218
Total current liabilities	161,705				150,105				161,705	150,105
Total debt	155,792				156,823				155,792	156,823
Capital Expenditures
Capital expenditures									142,371	124,282	64,753
Wireless
Revenue
Revenue									222,040	228,798	237,042
Wireline
Revenue
Revenue									225,763	188,019	86,485
Renewable Energy
Revenue
Revenue									20,467	21,608	21,040
Equipment and other
Revenue
Revenue									12,923	18,578	10,802
Corporate and Other
Revenue
Depreciation and amortization									4,659	6,030	4,948
Non-cash stock-based compensation									6,675	6,274	4,708
Operating income (loss)									(33,496)	(34,471)	(30,784)
Segment Assets
Cash, Cash equivalents, and Investments	76,627				131,664				76,627	131,664
Total current assets	93,497				135,745				93,497	135,745
Fixed assets, net	17,752				15,429				17,752	15,429
Total assets	184,050				170,505				184,050	170,505
Total current liabilities	13,816				18,838				13,816	18,838
Capital Expenditures
Capital expenditures									6,491	6,876
U.S. Telecom
Segment Assets
Goodwill	35,268				35,268				35,268	35,268	39,639
U.S. Telecom | Operating segments
Revenue
Revenue									155,724	176,726	182,986
Depreciation and amortization									25,601	24,471	22,239
Operating income (loss)									55,317	49,078	74,459
Segment Assets
Cash, Cash equivalents, and Investments	19,585				22,235				19,585	22,235
Total current assets	40,975				50,983				40,975	50,983
Fixed assets, net	99,462				129,274				99,462	129,274
Goodwill	35,269				35,268				35,269	35,268
Total assets	200,142				240,006				200,142	240,006
Total current liabilities	41,248				23,162				41,248	23,162
Capital Expenditures
Capital expenditures									22,230	31,983
U.S. Telecom | Operating segments | Wireless
Revenue
Revenue									140,636	148,053	155,390
U.S. Telecom | Operating segments | Wireline
Revenue
Revenue									12,656	26,448	25,241
U.S. Telecom | Operating segments | Equipment and other
Revenue
Revenue									2,432	2,225	2,355
International Telecom segment | Operating segments
Revenue
Revenue									304,603	258,276	151,343
Depreciation and amortization									50,007	40,492	24,883
Non-cash stock-based compensation									188	22
Operating income (loss)									28,468	35,436	28,200
Segment Assets
Cash, Cash equivalents, and Investments	110,700				97,681				110,700	97,681
Total current assets	190,396				143,201				190,396	143,201
Fixed assets, net	367,485				372,741				367,485	372,741
Goodwill	25,421				24,326				25,421	24,326
Total assets	629,007				597,454				629,007	597,454
Total current liabilities	91,887				95,502				91,887	95,502
Total debt	94,577				91,316				94,577	91,316
Capital Expenditures
Capital expenditures									80,912	62,808
International Telecom segment | Operating segments | Wireless
Revenue
Revenue									81,404	80,745	81,652
International Telecom segment | Operating segments | Wireline
Revenue
Revenue									213,107	161,571	61,244
International Telecom segment | Operating segments | Equipment and other
Revenue
Revenue									10,092	15,960	8,447
Renewable Energy
Segment Assets
Goodwill	3,279				3,279				3,279	3,279
Renewable Energy | Operating segments
Revenue
Revenue									20,866	22,001	21,040
Depreciation and amortization									6,667	4,987	4,820
Non-cash stock-based compensation									114	114	267
Operating income (loss)									5,179	(246)	6,720
Segment Assets
Cash, Cash equivalents, and Investments	8,120				27,378				8,120	27,378
Total current assets	18,060				37,440				18,060	37,440
Fixed assets, net	158,447				130,268				158,447	130,268
Goodwill	3,280				3,279				3,280	3,279
Total assets	192,406				190,253				192,406	190,253
Total current liabilities	14,754				12,603				14,754	12,603
Total debt	$ 61,215				$ 65,507				61,215	65,507
Capital Expenditures
Capital expenditures									32,738	22,615
Renewable Energy | Operating segments | Renewable Energy
Revenue
Revenue									20,467	21,608	$ 21,040
Renewable Energy | Operating segments | Equipment and other
Revenue
Revenue									$ 399	$ 393