SUPPLEMENTAL CONSOLIDATED FINANCIAL STATEMENT INFORMATION (Details) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) segment	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Number of business segments \| segment			1
Operating revenues	$ 24,076	$ 36,158	$ 75,240	$ 86,038
Deferred cost					$ 6,994	$ 2,991
Deferred costs incurred to fulfill contracts with customers	4,590	7,367	4,590	7,367
Total deferred costs amortized	7,542	7,248	20,447	14,247
Deferred revenue	8,538	7,103	8,538	7,103	$ 10,501	$ 6,314
Revenue recognized that was included in deferred revenue balances at beginning of period	1,284	1,628	8,177	5,311
United States
Operating revenues	22,046	35,288	59,682	73,065
Canada
Operating revenues	$ 2,030	$ 870	$ 15,558	$ 12,973

Amount of amortization expense for asset recognized from cost incurred to obtain or fulfill contract with customer.

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Amount, after accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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