Supplemental Financial Statement Information - Summary of Cash Equivalents and Short-Term Investments (Parenthetical) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents and Short-Term Investments
Cash And Restricted Cash [Line Items]
Cash	$ 328.1	$ 248.0
Restricted Cash and Cash Equivalents and Restricted Investments
Cash And Restricted Cash [Line Items]
Restricted cash	58.0	50.2
Prepaid Expenses and Other Current Assets
Cash And Restricted Cash [Line Items]
Restricted cash	$ 1.9	$ 1.4