REVENUE RECOGNITION, Contract Assets and Contract Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Contract with Customer, Asset and Liability [Abstract]
Accounts Receivable	$ 4,908	$ 6,071
Total Deferred Revenue	1,062	1,252
Tariff Revenue [Member]
Contract with Customer, Asset and Liability [Abstract]
Accounts Receivable	4,623	5,751
Contract Assets	2,272	2,367
Total Deferred Revenue	854	1,025
Refund Liability	3,772	3,298
Deferred Revenue	1,000
Non-Tariff Revenue [Member]
Contract with Customer, Asset and Liability [Abstract]
Accounts Receivable	285	320
Total Deferred Revenue	208	$ 227
Deferred Revenue	$ 189

For an unclassified balance sheet, the amount due from customers or clients for goods or services that have been delivered or sold in the normal course of business, reduced to their estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

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Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

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Amount of liability for consideration received or receivable from customer which is not included in transaction price, when consideration is expected to be refunded to customer.

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