Benefit Plans (Fair Values Of Nonvested Performance Shares And Performance Units) (Details)	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Performance Shares Liability Awards [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested, December 31 (in shares/awards)	68,307
Performance Units Liability Awards [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested, December 31 (in shares/awards)	16,801
2018 Grant [Member] | Performance Shares Liability Awards [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested, December 31 (in shares/awards)	68,307
Estimated payout percentage based on performance criteria	172.50%
Fair values of each nonvested award (in dollars per share) | $ / shares	$ 88.89
2018 Grant [Member] | Performance Units Liability Awards [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonvested, December 31 (in shares/awards)	16,801
Estimated payout percentage based on performance criteria	172.50%
Fair values of each nonvested award (in dollars per share) | $ / shares	$ 88.89