Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2019

Investments, Debt and Equity Securities [Abstract]

Schedule of Available-for-sale Securities Reconciliation [Table Text Block]

The amortized cost, gross unrealized holding gains, gross unrealized holding losses and fair value of available-for-sale debt securities by type of security at December 31, 2019 and December 31, 2018 were as follows:

	December 31, 2019
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses		Fair Value
Commercial paper	$	246.9	$	—	$	—	$	246.9
Corporate bonds	24.3		—		—		24.3
Other government related obligations:
U.S.	70.4		—		—		70.4
Bank certificates of deposit	27.4		—		—		27.4
Total available-for-sale debt securities	$	369.0	$	—	$	—	$	369.0

	December 31, 2018
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
Commercial paper	$	52.1	$	—	$	—		$	52.1
Corporate bonds	122.9		—		(0.1		)	122.8
Other government related obligations:
U.S.	17.5		—		—			17.5
Bank certificates of deposit	33.2		—		—			33.2
Total available-for-sale debt securities	$	225.7	$	—	$	(0.1	)	$	225.6

Available-for-sale Securities by Balance Sheet Location Classification [Table Text Block]

The fair values of available-for-sale debt securities by classification in the consolidated balance sheet were as follows:

	December 31, 2019		December 31, 2018
Cash and cash equivalents	$	328.1	$	43.8
Marketable securities	40.9		181.8
	$	369.0	$	225.6

Investments Classified by Contractual Maturity Date [Table Text Block]

The fair values of available-for-sale debt securities as of December 31, 2019, by contractual maturity, are summarized as follows:

	December 31, 2019
Due in one year or less	$	365.5
Due after one year through three years	3.5
Due after three years through five years	—
	$	369.0