Benefit Plans (Fair Values Of Nonvested Performance Shares And Performance Units) (Details) - $ / shares	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	206,868	223,511
Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	59,667	71,737
2018 Grant [Member] | Performance Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	74,163
Estimated payout percentage based on performance criteria	100.00%
Fair values of each nonvested award (in dollars per share)	$ 40.86
2018 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	19,840
Estimated payout percentage based on performance criteria	100.00%
Fair values of each nonvested award (in dollars per share)	$ 40.86
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	115.00%
Fair values of each nonvested award (in dollars per share)	$ 46.99
2017 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	18,600
Estimated payout percentage based on performance criteria	115.00%
Fair values of each nonvested award (in dollars per share)	$ 46.99
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	160.00%
Fair values of each nonvested award (in dollars per share)	$ 65.38
2016 Grant [Member] | Performance Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested awards at target (in shares/awards)	21,227
Estimated payout percentage based on performance criteria	160.00%
Fair values of each nonvested award (in dollars per share)	$ 65.38