Supplemental Oil And Gas Disclosures (Schedule Of Capitalized Costs And Costs Incurred On Oil And Gas Properties) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Capitalized costs:
Proved properties	$ 6,018,568	$ 5,712,813	$ 5,446,305
Unproved properties not being amortized	330,216	296,764	314,867
Capitalized costs gross	6,348,784	6,009,577	5,761,172
Accumulated depreciation, depletion, amortization, and impairment	(5,124,257)	(4,996,696)	(4,900,304)
Net capitalized costs	1,224,527	1,012,881	860,868
Costs incurred:
Unproved properties acquired	57,430	47,029	21,675
Proved properties acquired	15,158	47,638	564
Exploration	15,907	14,811	17,325
Development	280,692	160,941	80,582
Asset retirement obligation	(7,629)	(3,613)	(30,906)
Total costs incurred	$ 361,558	$ 266,806	$ 89,240