Note 1 - Description of Business and Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Oil and Gas Property Full Cost Method Period Increase (Decrease)	$ 100	$ 100
Unamortized Costs Capitalized Less Related Deferred Income Taxes Exceed Ceiling Limitations, Expense	$ 0	$ 0
Minimum [Member]
Property, Plant and Equipment, Useful Life	3 years
Maximum [Member]
Property, Plant and Equipment, Useful Life	5 years

The excess of unamortized costs capitalized within a cost center, less related deferred income taxes, over the cost center ceiling limitation, which is charged to expense for oil and gas producing companies that use full cost method of accounting for investments in oil and gas producing properties.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-10(c)(4)(ii))
-URI http://asc.fasb.org/extlink&oid=82851474&loc=d3e511914-122862

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 360
-Section S99
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=27015634&loc=d3e516453-122869

Name:	us-gaap_UnamortizedCostsCapitalizedLessRelatedDeferredIncomeTaxesExceedCeilingLimitationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration