Long-Term Debt and Credit Facility, Carrying Amount Table (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Principal amount, carrying amount and interest expense of notes
Principal amount	$ 225.0		$ 225.0
Carrying amount, net of discount	163.5		155.3
Remaining discount amortization period	1 year 3 months 18 days
Convertible Notes
Principal amount, carrying amount and interest expense of notes
Principal amount	175.0		175.0
Less: unamortized issuance discount	(11.5)	[1]	(19.7)
Carrying amount, net of discount	163.5		155.3
Contractual coupon interest	7.9		7.9		8.4
Amortization of discount	8.2		7.3		6.6
Amortization of deferred financing costs	1.2		1.2		1.2
Total interest expense	$ 17.3	[2]	$ 16.4	[2]	$ 16.2	[2]

[1] The remaining unamortized issuance discount at December 31, 2013 will be amortized over the next 1.3 years assuming no early conversion.

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