Long-Term Debt and Credit Facility, Carrying Amount Table (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Debt Instrument [Line Items]
Carrying amount, net of discount					$ 172.5
Convertible Debt
Debt Instrument [Line Items]
Contractual coupon interest	$ 0.0	$ 2.0	$ 2.0	$ 5.9
Amortization of discount	0.0	2.3	2.4	6.7
Amortization of deferred financing costs	0.0	0.3	0.3	0.9
Total interest expense	$ 0.0	$ 4.6	$ 4.7	$ 13.5