Long-Term Debt, Carrying Amount Table (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Principal amount, carrying amount and interest expense of notes
Principal amount	$ 225.0		$ 0
Carrying amount, net of discount	155.3		148.0
Remaining discount amortization period	2 years 3 months 18 days
Amortization of discount and deferred financing costs	9.8		8.6		4.5
Convertible Notes
Principal amount, carrying amount and interest expense of notes
Principal amount	175.0		175.0
Less: unamortized issuance discount	(19.7)	[1]	(27.0)
Carrying amount, net of discount	155.3		148.0
Contractual coupon interest	7.9		8.4		6.0
Amortization of discount and deferred financing costs	8.5		7.8		5.3
Total interest expense	$ 16.4	[2]	$ 16.2	[2]	$ 11.3	[2]

[1] The remaining unamortized issuance discount at December 31, 2012 will be amortized over the next 2.3 years assuming no early conversion.

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