Derivative And Financial Instruments (Changes In Fair Value) (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017 USD ($) item	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Derivative Instruments Gain Loss [Line Items]
Net gains (losses) on derivatives	$ 6,055	$ 3,990
Commodity Contract
Derivative Instruments Gain Loss [Line Items]
Beginning fair value of commodity derivatives	6,435	31,018	$ 31,018
Net premiums on derivative contracts			3,197
Ending fair value of commodity derivatives	$ 10,915		6,435
Number of counterparties | item	4
Oil | Commodity Contract
Derivative Instruments Gain Loss [Line Items]
Net gains (losses) on derivatives	$ 5,495		(8,355)
Net settlements on derivative contracts	(929)		(13,622)
Oil | Oil And Liquids Sales | Commodity Contract
Derivative Instruments Gain Loss [Line Items]
Net gains (losses) on derivatives	5,495	2,692
Natural Gas | Commodity Contract
Derivative Instruments Gain Loss [Line Items]
Net gains (losses) on derivatives	560		1,116
Net settlements on derivative contracts	(646)		$ (6,919)
Natural Gas | Natural Gas Sales | Commodity Contract
Derivative Instruments Gain Loss [Line Items]
Net gains (losses) on derivatives	$ 560	$ 1,298