Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Lowered statutory rate, percent	0.30%	13.70%	(1.10%)
Deferred tax assets		$ (205.2)
Valuation allowance	$ 552.5	607.8
Accrued and Other Current Liabilities [Member]
Operating Loss Carryforwards [Line Items]
Income taxes payable	0.4	$ 12.2
All U.S. and Portion of Icelandic Deferred Tax Assets [Member]
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 552.5