Income Taxes, Valuation allowance and tax carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income taxes
Valuation allowance, related to the foreign net operating loss carryforwards and U.S. state tax credits	$ 39.6	$ 37.2
Change in the valuation allowance, related to foreign net operating loss and foreign and U.S. state credit carryforwards	2.4	$ 18.7
Foreign
Income taxes
Loss carryforwards	139.6
Operating loss carryforwards to expire or be refunded	98.6
Tax credit carryforwards	2.8
Tax credit carryforwards to expire or be refunded	2.8
U.S. Federal
Income taxes
Loss carryforwards	3.5
Operating loss carryforwards to expire or be refunded	3.5
Tax credit carryforwards	32.7
Tax credit carryforwards to expire or be refunded	32.7
U.S. State
Income taxes
Loss carryforwards	45.9
Operating loss carryforwards to expire or be refunded	45.9
Tax credit carryforwards	12.4
Tax credit carryforwards to expire or be refunded	$ 6.8