Note 16 - Supplemental Oil and Gas Disclosures (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

Notes Tables

Capitalized Costs Relating to Oil and Gas Producing Activities Disclosure [Table Text Block]

	Years Ended December 31,
	2017			2018
Proved oil and gas properties	$	923,237		$	1,091,905
Unproved properties		-			-
Total		923,237			1,091,905
Accumulated depreciation, depletion, amortization and impairment		(706,537	)		(748,773	)
Net capitalized costs	$	216,700		$	343,132

Cost Incurred in Oil and Gas Property Acquisition, Exploration, and Development Activities Disclosure [Table Text Block]

	2016		2017		2018
Development costs	$	18,262	$	94,478	$	131,271
Exploration costs		12,529		8,509		-
Property acquisition costs		-		31,409		41,465
	$	30,791	$	134,396	$	172,736

Results of Operations for Oil and Gas Producing Activities Disclosure [Table Text Block]

		2016			2017			2018
Revenues	$	56,493		$	86,189		$	149,030
Production costs		(23,659	)		(22,425	)		(36,323	)
Depreciation, depletion and amortization		(22,803	)		(25,676	)		(42,237	)
Proved property impairment		(67,626	)		-			-
Results of operations from oil and gas producing activities (excluding corporate overhead and interest costs)	$	(57,595	)	$	38,088		$	72,488
Depletion rate per barrel of oil equivalent	$	10.08		$	9.52		$	11.80

Schedule of Proved Developed and Undeveloped Oil and Gas Reserve Quantities [Table Text Block]

										Oil
	Oil			NGL			Gas			Equivalents
	(MBbl)			(MBbl)			(MMcf)			(Mboe)
Change in Proved Reserves
Balance at December 31, 2015		24,131			6,556			75,027			43,190
Revisions of previous estimates		1,379			2,300			(1,537	)		3,424
Extensions and discoveries		1,183			157			1,179			1,537
Sales of minerals in place		(1,112	)		(6	)		(680	)		(1,232	)
Production		(1,372	)		(363	)		(3,160	)		(2,262	)
Balance at December 31, 2016		24,209			8,644			70,829			44,657
Revisions of previous estimates		259			1,269			19,311			4,747
Extensions and discoveries		14,533			2,813			14,534			19,768
Purchases of minerals in place		8			14			1,001			189
Sales of minerals in place		(364	)		(289	)		(3,958	)		(1,312	)
Production		(1,574	)		(476	)		(3,889	)		(2,698	)
Balance at December 31, 2017		37,071			11,975			97,828			65,351
Revisions of previous estimates		(4,206	)		(1,927	)		(2,618	)		(6,570	)
Extensions and discoveries		11,270			1,797			11,475			14,979
Purchases of minerals in place		688			-			1,137			877
Sales of minerals in place		(278	)		(1,303	)		(13,491	)		(3,829	)
Production		(2,308	)		(508	)		(4,587	)		(3,580	)
Balance at December 31, 2018		42,237			10,034			89,744			67,228

	Total
							Oil
	OIl		NGL		Gas		Equilavents
	(MBbl)		(MBbl)		(MMcf)		(Mboe)
Proved Developed Reserves:
December 31, 2016		7,818		2,568		27,792		15,018
December 31, 2017		10,820		3,794		39,974		21,720
December 31, 2018		13,586		3,804		43,271		24,602
Proved Undeveloped Reserves:
December 31, 2016		16,391		6,076		43,037		29,639
December 31, 2017		25,808		8,181		57,854		43,631
December 31, 2018		28,651		6,230		46,473		42,626

Standardized Measure of Discounted Future Cash Flows Relating to Proved Reserves Disclosure [Table Text Block]

	Years Ended December 31,
	2016			2017			2018
Future cash inflows	$	999,716		$	2,035,619		$	2,876,976
Future production costs		(357,917	)		(609,921	)		(849,063	)
Future development costs		(267,836	)		(461,619	)		(547,163	)
Future income tax expense (1)		-			(83,915	)		(181,224	)
Future net cash flows		373,963			880,164			1,299,526
Discount	$	(213,363	)	$	(474,423	)	$	(647,642	)
Standardized Measure of discounted future net cash relating to proved reserves	$	160,600		$	405,741		$	651,884

Schedule of Changes in Standardized Measure of Discounted Future Net Cash Flows [Table Text Block]

	Years Ended December 31,
	2016			2017			2018
Standardized Measure, beginning of year	$	197,251		$	160,600		$	405,741
Sales and transfers of oil and gas produced, net of production costs		(32,834	)		(63,764	)		(112,707	)
Net change in prices and development and production costs from prior year		(58,425	)		159,661			268,942
Extensions, discoveries, and improved recovery, less related costs		5,531			129,277			153,544
Sales of minerals in place		(4,433	)		(8,583	)		(39,253	)
Purchases of minerals in place		-			1,238			8,990
Revisions of previous estimates		12,317			31,044			(67,345	)
Change in timing and other		21,468			1,908			30,811
Change in future income tax expense		-			(21,700	)		(37,413	)
Accretion of discount		19,725			16,060			40,574
Standardized Measure, end of year	$	160,600		$	405,741		$	651,884

Oil and Gas Prices Considered in Standardized Measure of Discounted Future Net Cash Flows [Table Text Block]

	Years Ended December 31,
	2016		2017		2018
Oil (per Bbl) (1)	$	42.74	$	51.34	$	65.56
Gas (per MMbtu) (2)	$	2.50	$	2.99	$	3.05
Oil (per Bbl) (3)	$	35.54	$	46.83	$	56.95
Gas (per MMbtu) (4)	$	1.41	$	1.79	$	1.76
NGL's (per Bbl) (5)	$	5.17	$	13.19	$	19.95