Supplemental Oil And Gas Disclosures (Results Of Operations For Producing Activities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Oil and Gas Disclosures [Abstract]
Revenues	$ 429,119	$ 347,285	$ 282,742
Production costs	(131,328)	(113,344)	(103,568)
Depreciation, depletion, amortization, and impairment	(132,923)	(101,326)	(274,155)
Results of operations, income before income taxes	164,868	132,615	(94,981)
Income tax (expense) benefit	(42,915)	(52,078)	32,696
Results of operations for producing activities (excluding corporate overhead and financing costs)	$ 121,953	$ 80,537	$ (62,285)