Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Measurements [Abstract]

Schedule of financial assets and liabilities at fair value

(in thousands)	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
December 31, 2018
Asset:
Commodity derivatives	$	-	$	7,022	$	-	$	7,022
December 31, 2017
Asset:
Commodity derivatives	$	-	$	225	$	-	$	225
Liability:
Warrant derivative liability	$	-	$	-	$	2,017	$	2,017

Schedule of changes in fair value of financial instruments

(in thousands)	California Warrant			Appalachia Warrant			Total
Balance, December 31, 2016	$	-		$	-		$	-
Warrant liability		5,769			1,325			7,094
Unrealized (gain) loss included in warrant gain		(3,752	)		619			(3,133	)
Settlement of warrant liability		-			(1,944	)		(1,944	)
Balance, December 31, 2017	$	2,017		$	-		$	2,017
Unrealized (gain) included in warrant gain		(225	)		-			(225	)
Settlement of warrant liability		(1,792	)		-			(1,792	)
Balance, December 31, 2018	$	-		$	-		$	-