Unusual Items - Summary of Loss Incurred on Repurchase of Debt Instruments (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2016	Nov. 30, 2015	Nov. 30, 2014	Dec. 31, 2009
Unusual or Infrequent Item [Line Items]
Loss on 4 1/16% Debentures repurchased	$ 0.0	$ (34.5)	$ (1.9)	$ (60.8)
4 1/16% Convertible Subordinated Debentures [Member]
Unusual or Infrequent Item [Line Items]
Principal amount repurchased				59.6
Cash repurchase price				(119.9)
Write-off of deferred financing costs				(0.3)
Loss on 4 1/16% Debentures repurchased				$ (60.6)
Debt instrument interest rate stated percentage		4.0625%			4.0625%