Income Taxes Income Taxes - Reconciliation of the Expected Federal Income Tax at Statutory Rates (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Effective income tax rate reconciliation at federal statutory income tax rate, amount	$ 1.3	$ (13.5)	$ (2.3)
Effective income tax rate reconciliation, state and local income taxes, amount	(0.4)	(1.3)	0.2
Effective income tax rate reconciliation, change in deferred tax assets valuation allowance, amount	12.0	2.2	0.7
Effective income tax rate reconciliation, foreign income tax rate differential, amount	1.5	3.4	(0.8)
Effective income tax rate reconciliation, nondeductible expense, other, amount	0.0	0.0	8.4
Effective income tax rate reconciliation, nondeductible expense, amount	1.8	1.7	0.9
Effective income tax rate reconciliation, tax credit, amount	(3.6)	(2.4)	0.0
Effective income tax rate reconciliation, tax contingency, amount	2.4	1.2	(0.4)
Effective income tax rate reconciliation, nondeductible expense, share-based compensation cost, amount	0.7	3.8	(0.6)
Effective income tax rate reconciliation, change in enacted tax rate, amount	0.0	1.1	(1.3)
Effective income tax rate reconciliation Tax Cuts And Jobs Act transition tax on accumulated foreign earning	(0.6)	0.0	5.6
Effective income tax rate reconciliation Tax Cuts And Jobs Act U.S. taxation of foreign earnings	(1.1)	0.5	7.0
Effective income tax rate reconciliation, other adjustments, amount	0.0	0.0	(3.6)
Effective income tax rate reconciliation, other reconciling items, amount	0.0	(0.7)	(0.7)
Income tax expense (benefit)	$ 14.0	$ (4.0)	$ 13.1