Benefit Plans (Fair Values Of Nonvested Performance Shares And Performance Units) (Details) - $ / shares	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	205,963	223,511
Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	57,761	71,737
2018 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	73,258
Estimated payout percentage based on performance criteria	85.00%
Fair values of each nonvested award (in dollars per share)	$ 36.18
2018 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	19,196
Estimated payout percentage based on performance criteria	85.00%
Fair values of each nonvested award (in dollars per share)	$ 36.18
2017 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	65,350
Estimated payout percentage based on performance criteria	105.00%
Fair values of each nonvested award (in dollars per share)	$ 44.70
2017 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	18,062
Estimated payout percentage based on performance criteria	105.00%
Fair values of each nonvested award (in dollars per share)	$ 44.70
2016 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	67,355
Estimated payout percentage based on performance criteria	143.00%
Fair values of each nonvested award (in dollars per share)	$ 60.88
2016 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	20,503
Estimated payout percentage based on performance criteria	143.00%
Fair values of each nonvested award (in dollars per share)	$ 60.88