Significant Accounting Policies - Summary of Allowance for Doubtful Account (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning balance	$ (1.9)	$ (2.2)	$ (2.5)
Bad debt expense	(0.6)	(0.8)	(0.6)
Write-offs, net of recoveries	1.2	1.1	0.9
Ending balance	$ (1.3)	$ (1.9)	$ (2.2)