Debt (Narrative) (Details) (USD $)					3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Senior Unsecured Notes [Member]	Feb. 01, 2012 Senior Unsecured Notes [Member]	Mar. 31, 2012 Senior Secured Credit Facility [Member]	Mar. 31, 2012 Senior Secured Credit Facility [Member] Letters Of Credit [Member]	Mar. 31, 2012 Inventory Sublimit [Member] Senior Secured Credit Facility [Member]
Debt Instrument [Line Items]
Carrying value of senior unsecured notes	$ 350,981,000	$ 250,000,000
Fair value of senior unsecured notes	358,800,000	253,100,000
Debt instrument, principal amount			350,000,000	100,000,000
Debt instrument, stated rate			7.875%
Debt instrument, percentage of face value				101.00%
Debt instrument, effective interest rate			7.682%
Credit facility, amount outstanding					438,200,000		75,600,000
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						4,900,000
Maturity date of debt					Jun. 30, 2015
Total amount available for borrowings under credit facility					$ 331,900,000