Stock-Based Compensation (Schedule Of Restricted Stock Awards Stock Options And SAR) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized stock compensation expense	$ 15.3	[1]	$ 17.4	$ 16.1
Capitalized stock compensation cost for our oil and natural gas properties	3.5	[1]	3.7	3.5
Tax benefit on stock based compensation	5.8	[1]	$ 6.7	$ 6.2
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reduction in recognized stock compensation expense related to performance shares	3.2
Reduction in capitalized stock compensation cost for our oil and natural gas properties related to performance shares	0.2
Reduction in tax benefit on stock based compensation related to performance shares	$ 1.2

[1] Recognized stock compensation was reduced by $3.2 million, capitalized stock compensation cost for our oil and natural gas properties was reduced by $0.2 million, and the tax benefit was reduced by $1.2 million for lower expected payouts related to the performance shares.