Stock-Based Employee Compensation (Options Activity) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Options
Outstanding, beginning balance (in shares)	64,987
Granted (in shares)	0
Exercised (in shares)	(15,340)
Canceled (in shares)	0
Outstanding, ending balance (in shares)	49,647	64,987
Vested at December 31, 2020 (in shares)	49,647
Options Exercisable at December 31, 2020 (in shares)	49,647
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per share)	$ 41.22
Granted (in dollars per share)	0
Exercised (in dollars per share)	25.18
Canceled (in dollars per share)	0
Outstanding, ending balance (in dollars per share)	46.18	$ 41.22
Vested at December 31, 2020 (in dollars per share)	46.18
Options Exercisable at December 31, 2020 (in dollars per share)	$ 46.18
Weighted-Average Remaining Contractual Term
Outstanding (Years)	1 month 9 days	10 months 13 days
Vested at December 31, 2020 (Years)	1 month 9 days
Options Exercisable at December 31, 2020 (Years)	1 month 9 days
Aggregate Intrinsic Value
Outstanding	$ 1,355,000	$ 5,990,000
Vested at December 31, 2020	1,355,000
Options Exercisable at December 31, 2020	1,355,000
Total intrinsic value of stock options exercised	1,500,000	$ 8,100,000	$ 11,100,000
Stock Option
Aggregate Intrinsic Value
Total unrecognized compensation cost	$ 0