Income Taxes - Carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Carryforwards
Valuation allowance against deferred tax assets	$ 40.5	$ 36.6
UK
Carryforwards
Valuation allowance against deferred tax assets	8.3
UK | Capital loss carryforwards
Carryforwards
Tax credit carryforwards	3.4
Germany
Carryforwards
Net operating loss carryforwards	30.6
Valuation allowance against net operating loss carryforwards	13.0
Australia
Carryforwards
Net operating loss carryforwards	10.0
New Zealand
Carryforwards
Net operating loss carryforwards	1.7
Italy
Carryforwards
Net operating loss carryforwards	0.1
State | U.S.
Carryforwards
Net operating loss carryforwards	558.7
Net operating loss carryforwards utilized	86.3
Valuation allowance against net operating loss carryforwards	0.9
Federal and state | U.S.
Carryforwards
Tax credit carryforwards	5.4
Valuation allowance against tax credit carryforwards	0.4
Foreign | U.S.
Carryforwards
Tax credit carryforwards	31.5
Valuation allowance against tax credit carryforwards	$ 17.9