Share-Based Compensation (Summary of Stock Option Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Stock Options
Outstanding at Beginning of period (in shares)	571,380	1,406,371	2,626,487
Granted (in shares)		268,817
Exercised (in shares)	(118,094)	(1,102,830)	(1,219,820)
Forfeited (in shares)	(5,570)	(978)	(296)
Outstanding at End of period (in shares)	447,716	571,380	1,406,371
Stock options, exercisable (in shares)	268,504	300,000
Weighted-Average Exercise Price
Outstanding at Beginning of period (in dollars per share)	$ 43.84	$ 22.32	$ 27.74
Granted (in dollars per share)		66.68
Exercised (in dollars per share)	24.44	21.98	34.00
Forfeited (in dollars per share)	25.29	21.33	23.31
Outstanding at End of period (in dollars per share)	49.19	43.84	$ 22.32
Options exercisable, weighted average exercise price (in dollars per share)	$ 37.51	$ 23.55