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Balance Sheet Details - Short-term Marketable Securities, Available-for-Sale (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Equity investment in Tandem Diabetes Care, Inc
Amortized Cost	$ 2.0
Gross Unrealized Gains	36.0
Gross Unrealized Losses	0.0
Estimated Market Value	38.0
Debt securities, available for sale:
Amortized Cost	210.7	$ 1,086.7
Gross Unrealized Gains	0.0	0.5
Gross Unrealized Losses	(0.1)	(0.1)
Estimated Market Value	210.6	1,087.1
Amortized Cost	212.7
Gross Unrealized Gains	36.0
Gross Unrealized Losses	(0.1)
Estimated Market Value	248.6	1,087.1
U.S. government agencies
Debt securities, available for sale:
Amortized Cost	173.2	675.6
Gross Unrealized Gains	0.0	0.4
Gross Unrealized Losses	(0.1)	0.0
Estimated Market Value	173.1	676.0
Commercial paper
Debt securities, available for sale:
Amortized Cost	36.2	248.1
Gross Unrealized Gains	0.0	0.1
Gross Unrealized Losses	0.0	0.0
Estimated Market Value	36.2	248.2
Corporate debt
Debt securities, available for sale:
Amortized Cost	1.3	163.0
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	(0.1)
Estimated Market Value	$ 1.3	$ 162.9

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