Debt, Carrying Amount Table (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended					3 Months Ended
	Jun. 30, 2012 Convertible Notes		Jun. 30, 2011 Convertible Notes		Jun. 30, 2012 Convertible Notes		Jun. 30, 2011 Convertible Notes		Dec. 31, 2011 Convertible Notes	Jun. 30, 2012 Senior Notes		May 23, 2012 Senior Notes
Principal amount, carrying amount and interest expense of notes
Principal amount	$ 175.0				$ 175.0				$ 175.0			$ 225.0
Less: unamortized issuance discount	(23.4)				(23.4)				(27.0)
Carrying amount, net of discount	151.6				151.6				148.0
Contractual coupon interest	1.9		1.9		3.9		3.9			2.0
Amortization of discount and deferred financing costs	2.1		1.9		4.1		3.8			0.1
Total interest expense	$ 4.0	[1]	$ 3.8	[1]	$ 8.0	[1]	$ 7.7	[1]		$ 2.1	[2]

[1] A portion of the interest relating to the Convertible Notes is capitalized as Construction in progress

[2] A portion of the interest relating to the Senior Notes is capitalized as Construction in progress.