Fair Value Measurements Narrative (Details) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013 Senior Unsecured Notes [Member] $250 Million Senior Notes [Member]	Dec. 31, 2012 Senior Unsecured Notes [Member] $250 Million Senior Notes [Member]	Aug. 25, 2010 Senior Unsecured Notes [Member] $250 Million Senior Notes [Member]	Sep. 30, 2013 Senior Unsecured Notes [Member] $400 Million Senior Notes [Member]	Dec. 31, 2012 Senior Unsecured Notes [Member] $400 Million Senior Notes [Member]	Jun. 27, 2012 Senior Unsecured Notes [Member] $400 Million Senior Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Transfers Between Measurement Levels	$ 0	$ 0
Debt instrument face amount					250,000,000			400,000,000
Debt instrument fair value			$ 256,900,000	$ 271,600,000		$ 412,000,000	$ 442,000,000