Debt (Narrative) (Details) (USD $)	6 Months Ended			6 Months Ended
	Jun. 30, 2012 Senior Unsecured Notes [Member]	Jun. 30, 2012 Senior Unsecured Notes [Member]	Feb. 01, 2012 Senior Unsecured Notes [Member]	Jun. 30, 2012 Senior Secured Credit Facility [Member]	Jun. 30, 2012 Senior Secured Credit Facility [Member] Letters Of Credit [Member]	Jun. 30, 2012 Inventory Sublimit [Member] Senior Secured Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding				$ 445,000,000		$ 47,400,000
Credit facility, maximum borrowing capacity				775,000,000	100,000,000
Credit facility, aggregate maximum borrowing capacity				1,000,000,000
Letters of credit, outstanding amount					13,900,000
Credit facility and senior unsecured notes, maturity dates	Dec. 15, 2018			Jun. 30, 2015
Total amount available for borrowings under credit facility				316,100,000
Senior unsecured notes, principal amount		$ 350,000,000	$ 100,000,000
Senior unsecured notes, stated rate		7.875%
Senior unsecured notes, percentage of face value			101.00%
Senior unsecured notes, effective interest rate			7.682%