Significant Accounting Policies - Cash Flow Impact of New Accounting Pronouncements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities	$ 197.8	$ 215.1	$ 231.4
Cash, cash equivalents and restricted cash		85.5	83.0	$ 104.2
Net increase (decrease) in cash, cash equivalents, and restricted cash		2.0	(21.2)
Effect of exchange rate changes on cash	$ (0.8)	0.5	0.0
As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities		218.2	226.8
Cash, cash equivalents and restricted cash		54.3	48.7	74.5
Net increase (decrease) in cash, cash equivalents, and restricted cash		5.1	(25.8)
Effect of exchange rate changes on cash		0.5	0.0
Adoption of ASU 2016-18 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities		(3.1)	4.6
Cash, cash equivalents and restricted cash		31.2	34.3	$ 29.7
Net increase (decrease) in cash, cash equivalents, and restricted cash		(3.1)	4.6
Effect of exchange rate changes on cash		$ 0.0	$ 0.0