Debt (Revolving Credit Facility Under The Senior Credit Agreement) (Narrative) (Details) (USD $)	12 Months Ended			0 Months Ended		12 Months Ended						12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Feb. 07, 2014 Revolving Credit Facility [Member]	Jan. 08, 2014 Revolving Credit Facility [Member]	Dec. 31, 2013 Revolving Credit Facility [Member]	Mar. 14, 2013 Revolving Credit Facility [Member]	Jan. 28, 2013 Revolving Credit Facility [Member]	May 09, 2012 Revolving Credit Facility [Member]	Apr. 02, 2012 Revolving Credit Facility [Member]	Feb. 11, 2010 Revolving Credit Facility [Member]	Dec. 31, 2013 Minimum [Member] Eurodollar [Member]	Dec. 31, 2013 Minimum [Member] Base Rate [Member]	Dec. 31, 2013 Minimum [Member] Revolving Credit Facility [Member]	Dec. 31, 2013 Maximum [Member] Eurodollar [Member]	Dec. 31, 2013 Maximum [Member] Base Rate [Member]	Dec. 31, 2013 Maximum [Member] Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity						$ 770,000,000	$ 770,000,000	$ 730,000,000	$ 700,000,000	$ 600,000,000	$ 500,000,000
Basis spread on variable interest rate												1.875%	0.875%		2.375%	1.375%
Line of credit facility, commitment fee														0.375%			0.50%
Line of credit facility, outstanding						215,000,000
Revolving credit facility, effective interest rate						2.045%
Borrowings on the revolving credit facility					175,000,000	340,000,000
Repayments of revolving credit facility	225,000,000	484,000,000	270,000,000	390,000,000		225,000,000
Line of credit facility, remaining borrowing capacity				$ 770,000,000	$ 380,000,000	$ 555,000,000