Share-Based Compensation Share Based Compensation (Summmary of Restricted Stock Unit Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock Units Outstanding	1,709,813	2,047,158	1,798,543	1,769,420
Weighted Average Grant Price of Restricted Stock Units	$ 30.08	$ 25.08	$ 27.39	$ 25.64
Restricted Stock Units Granted	587,396	1,033,167	790,929
Weighted Average Grant Price of Restricted Stock Units Granted	$ 41.78	$ 21.69	$ 29.06
Restricted Stock Units Vested	(803,492)	(724,713)	(673,385)
Restricted Stock Units Forfeited	(121,249)	(59,839)	(88,421)
Weighted Average Grant Price of Restricted Stock Units Vested	$ 26.19	$ 25.88	$ 24.78
Weighted Average Grant Price of Restricted Stock Forfeited	$ 28.12	$ 26.28	$ 27.17