Stock Based Compensation (Performance Units Information) (Details) (Performance Units [Member], USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Performance Units [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	802,118
Shares, Granted	358,265
Shares, Vested	(382,504)
Shares, Canceled	(12,246)
Shares, Outstanding at End of Year	765,633	802,118
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	$ 33.25
Shares, Granted, Weighted Average Grant Date Fair Value	$ 38.94	$ 35.07	$ 31.25
Shares, Vested, Weighted Average Grant Date Fair Value	$ 31.25
Shares, Cancelled, Weighted Average Grant Date Fair Value	$ 36.45
Shares, Outstanding at End of Year, Weighted Average Grant Date Fair Value	$ 36.86	$ 33.25
Shares, Outstanding at End of Year, Weighted Average Remaining Years Contractual Term	1 year 6 months 6 days
Shares, Outstanding at End of Year, Aggregate Intrinsic Value	$ 31,704,863