REVENUE RECOGNITION AND RECEIVABLES - Contract Assets and Liabilities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Contract Assets and Liabilities
Contract Asset - current	$ 2,413
Change in contract asset - current	(38)
Contract Asset - current	$ 2,375
% of change in contract asset - current	(2.00%)
Contract asset, noncurrent	$ 905
Change in contract Asset - noncurrent	(89)
Contract asset, noncurrent	$ 816
% of change in contract Asset - noncurrent	(10.00%)
Contract liability- current	$ (15,044)
Change in contract liabilities - current	(4,327)
Contract liability- current	$ (19,371)
% of change in contract liabilities - current	29.00%
Contract liability- noncurrent	$ (5,450)
Change in contract liabilities - noncurrent	257
Contract liability- noncurrent	$ (5,193)
% of change in contract liabilities - Noncurrent	(5.00%)
Net contract liability	$ (17,176)
Change in net contract liability	(4,197)
Net contract liability	$ (21,373)
% of change in net contract liability	24.00%
Revenue recognized related to contract liability	$ 12,000
Amortization of contract assets	700
Revenue recognized in the period related to performance obligations that were satisfied or partially satisfied in previous periods	$ 0
Retail revenue period for billing postpaid customers in advance	1 month