Long-Term Debt and Credit Facility, Carrying Amount Table (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Principal amount, carrying amount and interest expense of notes
Carrying amount, net of discount					$ 172.5
Convertible Notes
Principal amount, carrying amount and interest expense of notes
Contractual coupon interest	$ 0.0	$ 1.9	$ 2.0	$ 3.9
Amortization of discount	0.0	2.3	2.4	4.4
Amortization of deferred financing costs	0.0	0.3	0.3	0.6
Total interest expense	$ 0.0	$ 4.5	$ 4.7	$ 8.9