Long-Term Debt and Credit Facility, Carrying Amount Table (Details) (Convertible Notes, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Convertible Notes
Principal amount, carrying amount and interest expense of notes
Principal amount	$ 175.0		$ 175.0
Less: unamortized issuance discount	0		(2.5)
Carrying amount, net of discount	175.0		172.5
Contractual coupon interest	2.0	2.0
Amortization of discount	2.4	2.1
Amortization of deferred financing costs	0.3	0.3
Total interest expense	$ 4.7	$ 4.4