Share-Based Compensation and Benefit Plans (Summary of Restricted Stock) (Details) - Restricted stock [Member] - $ / shares shares in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-Based Compensation and Benefit Plans
Restricted stock granted during period, weighted-average grant date fair value		$ 264.24	$ 208.56	$ 147.23
Shares withheld to cover employees' taxes upon vesting		2
Employee [Member]
Share-Based Compensation and Benefit Plans
Non-vested restricted stock at beginning of the year, weighted-average grant date fair value		$ 128.27
Restricted stock granted during period, weighted-average grant date fair value		256.34
Restricted stock vested during the period, weighted-average grant date fair value	[1]	140.91
Restricted stock forfeited during the period, weighted-average grant date fair value		150.85
Non-vested restricted stock at the end of the year, weighted-average grant date fair value		$ 204.33	$ 128.27
Employee [Member] | Performance shares [Member]
Share-Based Compensation and Benefit Plans
Non-vested restricted stock beginning balance, shares		7
Restricted stock granted during the period, shares		1
Restricted stock vested during the period, shares	[1]	(5)
Restricted stock forfeited during the period, shares		0
Non-vested restricted stock ending balance, shares		3	7
Director [Member]
Share-Based Compensation and Benefit Plans
Non-vested restricted stock at beginning of the year, weighted-average grant date fair value		$ 167.73
Restricted stock granted during period, weighted-average grant date fair value		268.54
Restricted stock vested during the period, weighted-average grant date fair value		149.49
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		$ 222.77	$ 167.73
Director [Member] | Performance shares [Member]
Share-Based Compensation and Benefit Plans
Non-vested restricted stock beginning balance, shares		7
Restricted stock granted during the period, shares		2
Restricted stock vested during the period, shares		(3)
Restricted stock forfeited during the period, shares		0
Non-vested restricted stock ending balance, shares		6	7

[1] Includes two thousand shares withheld to cover employees’ taxes upon vesting.