Long-Term Debt and Credit Facility, Carrying Amount Table (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2013
Principal amount, carrying amount and interest expense of notes
Carrying amount, net of discount	$ 165.7				$ 163.5
Convertible Notes
Principal amount, carrying amount and interest expense of notes
Principal amount	175.0				175.0
Less: unamortized issuance discount	(9.3)				(11.5)
Carrying amount, net of discount	165.7				163.5
Contractual coupon interest	2.0		2.0
Amortization of discount	2.1		1.9
Amortization of deferred financing costs	0.3		0.3
Total interest expense	$ 4.4	[1]	$ 4.2	[1]

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