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Balance Sheet Accounts - Summary of Cash and Cash Equivalents and Grantor Trust by Investment Type (Details) - USD ($)
$ in Millions
Mar. 31, 2017
Dec. 31, 2016
Mar. 31, 2016
Dec. 31, 2015
Cash and Cash Equivalents [Line Items]        
Cash and cash equivalents $ 382.1 $ 410.3 $ 155.5 $ 208.5
Grantor trust (included as a component of other current and noncurrent assets) 7.6      
Total investment 389.7      
Cash and Cash Equivalents        
Cash and Cash Equivalents [Line Items]        
Cash and cash equivalents 261.7      
Grantor trust (included as a component of other current and noncurrent assets) 0.0      
Total investment 261.7      
Money Market Funds        
Cash and Cash Equivalents [Line Items]        
Cash and cash equivalents 120.4      
Grantor trust (included as a component of other current and noncurrent assets) 7.6      
Total investment $ 128.0