Debt (Narrative) (Details) (USD $)	1 Months Ended	3 Months Ended				3 Months Ended
	Mar. 31, 2013 Line of Credt	Dec. 27, 2013 Line of Credt	Dec. 27, 2013 Senior Notes	Apr. 30, 2013 Senior Notes 3.50% Senior Note	Apr. 30, 2013 Senior Notes 4.75% Senior Note	Dec. 27, 2013 Line of Credt LIBOR	Mar. 31, 2013 Letter of Credit Line of Credt
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 250,000,000						$ 150,000,000
Term of debt instrument	5 years		10 years
Variable interest rate						1.50%
Facility fees for letters of credit		0.25%
Letters of credit outstanding		0.0
Borrowings, outstanding		0
Face amount				$ 300,000,000	$ 600,000,000
Stated interest rate				3.50%	4.75%