Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2020

Investments, Debt and Equity Securities [Abstract]

Realized Gain (Loss) on Investments

The proceeds from maturities and sales of available-for-sale debt securities and resulting realized gains and losses are summarized below. In the second quarter of 2020, we liquidated all of our available-for-sale debt securities to fund the acquisition of Portola, which closed on July 2, 2020.

	Three months ended				Six months ended
	June 30,				June 30,
	2020		2019		2020		2019
Proceeds from maturities and sales (1)	$	204.5	$	798.6	$	1,016.9	$	1,626.3
Realized gains	$	—	$	—	$	—	$	—
Realized losses	$	—	$	—	$	—	$	—
(1) Proceeds from maturities and sales of available-for-sale debt securities include securities previously classified as cash and cash equivalents and marketable securities in the condensed consolidated balance sheet

Schedule of Available-for-sale Securities Reconciliation

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

Available-for-sale Securities by Balance Sheet Location Classification

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

	June 30, 2020		December 31, 2019
Cash and cash equivalents	$	—	$	328.1
Marketable securities	—		40.9
	$	—	$	369.0