Marketable Securities

Marketable securities as of December 31, 2018 and 2017 consist of both available-for-sale debt securities of investment grade issuers (see below and Note 5) as well as equity securities of publicly traded companies (see Note 5).

The following tables summarize the Company's investments in available-for-sale debt securities:



	Amortized		Unrealized					Fair
As of December 31, 2018	Cost Basis		Gains		Losses			Value
Available-for-sale debt securities:
Corporate bonds	$	2,734.8	$	1.0	$	(17.4	)	$	2,718.4
U.S. government and government agency obligations	110.4		—		(1.0		)	109.4
Sovereign bonds	7.6		—		—			7.6
Commercial paper	113.8		—		—			113.8
Certificates of deposit	60.0		—		—			60.0
	$	3,026.6	$	1.0	$	(18.4	)	$	3,009.2



As of December 31, 2017
Available-for-sale debt securities:
Corporate bonds	$	1,718.0	$	2.2	$	(7.7	)	$	1,712.5
U.S. government and government agency obligations	186.7		—		(1.2		)	185.5
Municipal and sovereign bonds	4.6		—		—			4.6
Commercial paper	107.0		—		—			107.0
Certificates of deposit	11.0		—		—			11.0
	$	2,027.3	$	2.2	$	(8.9	)	$	2,020.6

The Company classifies its investments in available-for-sale debt securities based on their contractual maturity dates. The available-for-sale debt securities listed as of December 31, 2018 mature at various dates through November 2023. The fair values of available-for-sale debt security investments by contractual maturity consist of the following:



	As of December 31,
	2018		2017
Maturities within one year	$	1,342.2	$	593.8
Maturities after one year through five years	1,667.0		1,426.8
	$	3,009.2	$	2,020.6

The following table shows the fair value of the Company's available-for-sale debt securities that have unrealized losses and that are deemed to be only temporarily impaired, aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position.



	Less than 12 Months					12 Months or Greater					Total
As of December 31, 2018	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Corporate bonds	$	1,482.6	$	(6.1	)	$	801.6	$	(11.3	)	$	2,284.2	$	(17.4	)
U.S. government and government agency obligations	—		—			99.1		(1.0		)	99.1		(1.0		)
	$	1,482.6	$	(6.1	)	$	900.7	$	(12.3	)	$	2,383.3	$	(18.4	)

As of December 31, 2017
Corporate bonds	$	931.0	$	(4.9	)	$	256.8	$	(2.8	)	$	1,187.8	$	(7.7	)
U.S. government and government agency obligations	110.5		(0.4		)	67.9		(0.8		)	178.4		(1.2		)
	$	1,041.5	$	(5.3	)	$	324.7	$	(3.6	)	$	1,366.2	$	(8.9	)

There were no other-than-temporary impairment charges recorded with respect to the Company's investments during 2018 and 2017. During the year ended December 31, 2016, the Company recorded an other-than-temporary impairment charge of $9.8 million related to its investment in an equity security.

Realized gains and losses on sales of marketable securities were not material for the years ended December 31, 2018, 2017, and 2016.

With respect to marketable securities, for the years ended December 31, 2018, 2017, and 2016, amounts reclassified from Accumulated other comprehensive (loss) income into Other income (expense), net were related to realized gains and losses on sales and the 2016 impairment charge on the equity security described above. The Company adopted ASU 2016-01 (see Note 1) during the first quarter of 2018; as a result, there were $41.9 million of net unrealized losses on equity securities recognized in Other income (expense), net for the year ended December 31, 2018. During the years ended December 31, 2017 and 2016, we recorded net unrealized gains of $14.7 million and net unrealized losses of $22.6 million, respectively, on equity securities in Other comprehensive (loss) income.