SEGMENT REPORTING (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment reporting
Number of reportable segments | segment									3
Revenue
Revenue	$ 123,702	$ 111,739	$ 109,098	$ 110,905	$ 112,085	$ 115,616	$ 107,721	$ 103,300	$ 455,444	$ 438,722	$ 451,207
Depreciation and amortization									88,311	89,125	85,719
Non-cash stock-based compensation									5,912	6,384	6,420
Operating income (loss)	(14,700)	$ 9,557	$ 7,024	$ 7,299	(1,739)	$ 10,248	$ 2,754	$ 2,114	9,180	13,377	61,023
Segment Assets
Cash, Cash equivalents, and Investments	103,925				161,703				103,925	161,703
Total current assets	240,065				228,723				240,065	228,723
Fixed assets, net	536,462				605,581				536,462	605,581
Goodwill	60,691				60,691				60,691	60,691	63,970
Total assets	1,083,711				1,130,726				1,083,711	1,130,726
Total current liabilities	147,928				119,669				147,928	119,669
Total debt	72,823				86,426				72,823	86,426
Capital Expenditures
Capital expenditures									75,323	72,725
Communication services
Revenue
Revenue									433,509	428,108	425,323
Mobility
Revenue
Revenue									92,762	95,092	96,911
Fixed
Revenue
Revenue									252,644	238,745	221,625
Carrier services
Revenue
Revenue									86,568	92,976	104,707
Other
Revenue
Revenue									1,535	1,295	2,080
Other
Revenue
Revenue									21,935	10,614	25,884
Renewable Energy
Revenue
Revenue									4,555	5,534	22,158
Managed Services
Revenue
Revenue									6,467	5,080	3,726
Construction
Revenue
Revenue									10,913
Corporate and Other
Revenue
Depreciation and amortization									6,486	6,708	5,626
Non-cash stock-based compensation									5,586	5,892	6,227
Operating income (loss)									(32,523)	(34,365)	(34,252)
Segment Assets
Cash, Cash equivalents, and Investments	26,845				55,284				26,845	55,284
Total current assets	27,887				55,485				27,887	55,485
Fixed assets, net	12,857				21,453				12,857	21,453
Total assets	136,035				184,419				136,035	184,419
Total current liabilities	22,815				14,375				22,815	14,375
Capital Expenditures
Capital expenditures									3,613	6,758
International Telecom
Segment Assets
Goodwill	24,326				24,326				24,326	24,326	24,326
International Telecom | Operating segments
Revenue
Revenue									328,633	324,539	313,569
Depreciation and amortization									56,284	55,993	48,889
Non-cash stock-based compensation									49	405	88
Operating income (loss)									58,064	46,921	45,022
Segment Assets
Cash, Cash equivalents, and Investments	45,848				43,125				45,848	43,125
Total current assets	107,315				91,497				107,315	91,497
Fixed assets, net	449,888				466,523				449,888	466,523
Goodwill	25,421				25,421				25,421	25,421
Total assets	642,834				647,228				642,834	647,228
Total current liabilities	80,875				77,644				80,875	77,644
Total debt	72,823				86,426				72,823	86,426
Capital Expenditures
Capital expenditures									38,895	42,029
International Telecom | Operating segments | Communication services
Revenue
Revenue									322,166	319,459	309,843
International Telecom | Operating segments | Mobility
Revenue
Revenue									83,136	84,560	85,152
International Telecom | Operating segments | Fixed
Revenue
Revenue									230,375	224,534	213,765
International Telecom | Operating segments | Carrier services
Revenue
Revenue									7,120	9,070	8,846
International Telecom | Operating segments | Other
Revenue
Revenue									1,535	1,295	2,080
International Telecom | Operating segments | Other
Revenue
Revenue									6,467	5,080	3,726
International Telecom | Operating segments | Managed Services
Revenue
Revenue									6,467	5,080	3,726
US Telecom
Segment Assets
Goodwill	35,268				35,268				35,268	35,268	35,268
US Telecom | Operating segments
Revenue
Revenue									122,256	108,649	115,480
Depreciation and amortization									23,325	23,119	24,615
Non-cash stock-based compensation									15
Operating income (loss)									7,388	8,064	36,813
Segment Assets
Cash, Cash equivalents, and Investments	26,921				38,240				26,921	38,240
Total current assets	65,806				54,207				65,806	54,207
Fixed assets, net	73,717				69,184				73,717	69,184
Goodwill	35,270				35,270				35,270	35,270
Total assets	265,797				222,356				265,797	222,356
Total current liabilities	43,200				24,905				43,200	24,905
Capital Expenditures
Capital expenditures									29,883	17,490
US Telecom | Operating segments | Communication services
Revenue
Revenue									111,343	108,649	115,480
US Telecom | Operating segments | Mobility
Revenue
Revenue									9,626	10,532	11,759
US Telecom | Operating segments | Fixed
Revenue
Revenue									22,269	14,211	7,860
US Telecom | Operating segments | Carrier services
Revenue
Revenue									79,448	83,906	95,861
US Telecom | Operating segments | Other
Revenue
Revenue									10,913
US Telecom | Operating segments | Construction
Revenue
Revenue									10,913
Renewable Energy
Segment Assets
Goodwill	0				0				0	0	3,279
Renewable Energy | Operating segments
Revenue
Revenue									4,555	5,534	22,158
Depreciation and amortization									2,216	3,305	6,589
Non-cash stock-based compensation									262	87	105
Operating income (loss)									(23,749)	(7,243)	13,440
Segment Assets
Cash, Cash equivalents, and Investments	4,311				25,054				4,311	25,054
Total current assets	39,057				27,534				39,057	27,534
Fixed assets, net					48,421					48,421
Total assets	39,045				76,723				39,045	76,723
Total current liabilities	$ 1,038				$ 2,745				1,038	2,745
Capital Expenditures
Capital expenditures									2,932	6,448
Renewable Energy | Operating segments | Other
Revenue
Revenue									4,555	5,534	22,158
Renewable Energy | Operating segments | Renewable Energy
Revenue
Revenue									$ 4,555	$ 5,534	$ 22,158