Share-Based Compensation Share Based Compensation (Summmary of Restricted Stock Unit Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock Units Outstanding	1,400,699	1,709,813	2,047,158	1,798,543
Weighted Average Grant Price of Restricted Stock Units	$ 37.65	$ 30.08	$ 25.08	$ 27.39
Restricted Stock Units Granted	461,305	587,396	1,033,167
Weighted Average Grant Price of Restricted Stock Units Granted	$ 53.17	$ 41.78	$ 21.69
Restricted Stock Units Vested	(699,920)	(803,492)	(724,713)
Restricted Stock Units Forfeited	(70,499)	(121,249)	(59,839)
Weighted Average Grant Price of Restricted Stock Units Vested	$ 29.56	$ 26.19	$ 25.88
Weighted Average Grant Price of Restricted Stock Forfeited	$ 35.95	$ 28.12	$ 26.28