Stock Based Compensation (Restricted Stock Units Activity) (Details) (Restricted Stock Units (RSUs) [Member], USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Shares, Outstanding at Beginning of Year	1,047,569
Shares, Granted	356,240
Shares, Vested	(325,504)
Shares, Canceled	(9,276)
Shares, Outstanding at End of Year	1,069,029	1,047,569
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Shares, Outstanding at Beginning of Year, Weighted Average Grant Date Fair Value	$ 31.30
Shares, Granted, Weighted Average Grant Date Fair Value	$ 35.16	$ 31.41	$ 30.95
Shares, Vested, Weighted Average Grant Date Fair Value	$ 31.57
Shares, Canceled, Weighted Average Grant Date Fair Value	$ 33.95
Shares, Outstanding at End of Year, Weighted Average Grant Date Fair Value	$ 32.49	$ 31.30
Shares, Outstanding at End of Year, Weighted Average Remaining Years Contractual Term	1 year 1 month 5 days
Shares, Outstanding at End of Year, Aggregate Intrinsic Value	$ 44,268,491