Cash, Cash Equivalents, and Marketable Debt Securities (Tables)

12 Months Ended

Dec. 31, 2020

Cash Cash Equivalents And Short Term Investments [Abstract]

Schedule of Cash and Available-For-Sale Debt Securities by Major Asset Category

The following table shows the Company’s cash and available-for-sale (AFS) debt securities by major asset category at December 31, 2020 and 2019 (in millions):

	December 31, 2020
	Adjusted Cost Basis		Unrealized Gain		Unrealized Loss		Fair Value		Cash and Cash Equivalents		Short-Term Marketable Debt Securities		Long-Term Marketable Debt Securities
Cash and cash equivalents	$	970.5	$	—	$	—	$	970.5	$	970.5	$	—	$	—
Level 1 ^(a):
Money market funds		0.6		—		—		0.6		0.6		—		—
U.S. Treasury securities		28.1		0.2		—		28.3		—		18.9		9.4
Subtotal		28.7		0.2		—		28.9		0.6		18.9		9.4
Level 2 ^(b):
Certificates of deposit		5.9		—		—		5.9		1.1		4.8		—
Commercial paper		3.2		—		—		3.2		1.0		2.2		—
U.S. government agency securities		6.6		—		—		6.6		—		2.6		4.0
Corporate debt securities		107.5		0.3		—		107.8		1.4		77.1		29.3
Subtotal		123.2		0.3		—		123.5		3.5		86.7		33.3
Total	$	1,122.4	$	0.5	$	—	$	1,122.9	$	974.6	$	105.6	$	42.7

	December 31, 2019
	Adjusted Cost Basis		Unrealized Gain		Unrealized Loss		Fair Value (c)		Cash and Cash Equivalents		Short-Term Marketable Debt Securities		Long-Term Marketable Debt Securities
Cash and cash equivalents	$	675.6					$	675.6	$	675.6	$	—	$	—
Level 1 ^(a):
Money market funds		0.1		—		—		0.1		0.1		—		—
U.S. Treasury securities		27.1		—		—		27.1		3.1		11.5		12.5
Subtotal		27.2		—		—		27.2		3.2		11.5		12.5
Level 2 ^(b):
Certificates of deposit		3.9		—		—		3.9		—		3.9		—
Commercial paper		5.6		—		—		5.6		0.7		4.9		—
U.S. government agency securities		7.0		—		—		7.0		—		3.0		4.0
Corporate debt securities		106.2		—		—		106.2		—		64.6		41.6
Subtotal		122.7		—		—		122.7		0.7		76.4		45.6
Total	$	825.5	$	—	$	—	$	825.5	$	679.5	$	87.9	$	58.1

(a)

Valuations based on quoted prices for identical assets and liabilities in active markets.

(b)

Valuations based on observable inputs other than quoted prices included in Level 1, such as quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data.

(c)

Unrealized gains and losses were insignificant as of December 31, 2019. Therefore, the fair value approximates the adjusted cost basis for each major asset category.

Schedule of Marketable Debt Securities in Continuous Loss Position

The following table provides information about the Company’s marketable debt securities that have been in a continuous loss position as of December 31, 2020 and 2019 (in millions, except number of marketable debt securities in a loss position):

	December 31, 2020						December 31, 2019
	Fair Value of Marketable Debt Securities		Number of Marketable Debt Securities in a Loss Position		Unrealized Losses (d)		Fair Value of Marketable Debt Securities		Number of Marketable Debt Securities in a Loss Position		Unrealized Losses (d)
Corporate debt securities	$	42.9		56	$	—	$	63.3		61	$	—
Commercial paper		2.2		1		—		0.8		1		—
U.S. Treasury securities		1.7		3		—		14.0		9		—
Certificates of deposit		1.3		2		—		—		—		—
	$	48.1		62	$	—	$	78.1		71	$	—

(d)

Unrealized losses were insignificant for the periods ended December 31, 2020 and 2019.