Derivative And Financial Instruments (Effect On Statement Of Operations) (Details) - Commodity Contract - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Embedded Derivative [Line Items]
Net gains (losses) on derivatives	$ (4,524)	$ (1,937)
Oil reserves
Embedded Derivative [Line Items]
Net gains (losses) on derivatives	(4,484)	(1,939)	$ 1,400
Natural gas
Embedded Derivative [Line Items]
Net gains (losses) on derivatives	$ (40)	$ 2	$ (84)