Marketable Securities

12 Months Ended

Dec. 31, 2019

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable Securities

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

The aggregate fair value of available-for-sale debt securities in an unrealized loss position as of December 31, 2019 and December 31, 2018 was $21.5 and $128.7, respectively. We did not have any investments in a continuous unrealized loss position for more than twelve months as of December 31, 2019 and December 31, 2018. As of December 31, 2019, we believe that the cost basis of our available-for-sale debt securities is recoverable.

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

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

We sponsor a nonqualified deferred compensation plan which allows certain highly-compensated employees to elect to defer income to future periods. Participants in the plan earn a return on their deferrals based on several investment options, which mirror returns on underlying mutual fund investments. We choose to invest in the underlying mutual fund investments to offset the liability associated with our nonqualified deferred compensation plan. These mutual fund investments are valued at net asset value per share and are carried at fair value with gains and losses included in investment income. The changes in the underlying liability to the employee are recorded in operating expenses. As of December 31, 2019 and December 31, 2018, the fair value of these investments was $23.1 and $16.5, respectively.

We utilize the specific identification method in computing realized gains and losses. Realized gains and losses on our marketable securities were not material for the years ended December 31, 2019, 2018 and 2017.