Share-Based Compensation and Benefit Plans (Summary of Restricted Stock) (Details) - Restricted stock [Member] - $ / shares shares in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-Based Compensation and Benefit Plans
Restricted stock granted during period, weighted-average grant date fair value		$ 263.89	$ 253.78	$ 264.24
Shares withheld to cover employees' taxes upon vesting		1
Employee [Member]
Share-Based Compensation and Benefit Plans
Non-vested restricted stock at beginning of the year, weighted-average grant date fair value		$ 244.06
Restricted stock granted during period, weighted-average grant date fair value		262.38
Restricted stock vested during the period, weighted-average grant date fair value	[1]	232.30
Restricted stock forfeited during the period, weighted-average grant date fair value		0.00
Non-vested restricted stock at the end of the year, weighted-average grant date fair value		$ 260.42	$ 244.06
Employee [Member] | Performance shares [Member]
Share-Based Compensation and Benefit Plans
Non-vested restricted stock beginning balance, shares		3
Restricted stock granted during the period, shares		2
Restricted stock vested during the period, shares	[1]	(1)
Restricted stock forfeited during the period, shares		0
Non-vested restricted stock ending balance, shares		4	3
Director [Member]
Share-Based Compensation and Benefit Plans
Non-vested restricted stock at beginning of the year, weighted-average grant date fair value		$ 250.85
Restricted stock granted during period, weighted-average grant date fair value		265.41
Restricted stock vested during the period, weighted-average grant date fair value		248.53
Restricted stock forfeited during the period, weighted-average grant date fair value		0.00
Non-vested restricted stock at the end of the year, weighted-average grant date fair value		$ 261.07	$ 250.85
Director [Member] | Performance shares [Member]
Share-Based Compensation and Benefit Plans
Non-vested restricted stock beginning balance, shares		5
Restricted stock granted during the period, shares		3
Restricted stock vested during the period, shares		(3)
Restricted stock forfeited during the period, shares		0
Non-vested restricted stock ending balance, shares		5	5

[1] Includes less than one thousand shares withheld to cover employees’ taxes upon vesting.