Note 2 - Summary of Significant Accounting Policies (Details Textual) shares in Thousands	12 Months Ended
Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares
Available-for-sale Securities, Accumulated Gross Unrealized Gain (Loss), before Tax, Total	$ 0	$ 0
Unrecognized Tax Benefits, Ending Balance	$ 0	$ 0
Weighted Average Number of Shares Outstanding, Diluted, Total \| shares	0	0
Current Year Inflation Rate	4.08%
Change In Present Value, Percent	3.25%
Customer Concentration Risk [Member] \| Revenue Benchmark [Member]
Number of Major Customers	2	2
Concentration Risk, Percentage	27.00%	30.00%
Domestic Tax Authority [Member] \| Internal Revenue Service (IRS) [Member]
Open Tax Year	2016 2017 2018
Oil and Gas [Member]
Contract with Customer, Asset, after Allowance for Credit Loss, Total	$ 366,148	$ 346,711

The percentage by which the liability is increased annually for the change in its present value.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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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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Tax year that remains open to examination under enacted tax laws, in CCYY format.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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