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

3 Months Ended

Mar. 31, 2022

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 March 31, 2022 and December 31, 2021 (in millions):

	March 31, 2022
	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	$	627.4	$	—	$	—		$	627.4	$	627.4	$	—	$	—
Level 1 (a):
U.S. Treasury securities		22.9		—		(0.3	)		22.6		—		12.7		9.9
Money market funds		1.2		—		—			1.2		1.2		—		—
Subtotal		24.1		—		(0.3	)		23.8		1.2		12.7		9.9
Level 2 (b):
Corporate debt securities		122.3		—		(1.6	)		120.7		—		63.6		57.1
U.S. government agency securities		5.6		—		(0.1	)		5.5		—		4.0		1.5
Certificates of deposit		1.0		—		—			1.0		—		1.0		—
Subtotal		128.9		—		(1.7	)		127.2		—		68.6		58.6
Total	$	780.4	$	—	$	(2.0	)	$	778.4	$	628.6	$	81.3	$	68.5

	December 31, 2021
	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	$	612.3	$	—	$	—		$	612.3	$	612.3	$	—	$	—
Level 1 (a):
U.S. Treasury securities		26.4		—		(0.1	)		26.3		2.0		14.7		9.6
Money market funds		0.9		—		—			0.9		0.9		—		—
Subtotal		27.3		—		(0.1	)		27.2		2.9		14.7		9.6
Level 2 (b):
Corporate debt securities		118.9		—		(0.3	)		118.6		3.5		66.0		49.1
U.S. government agency securities		4.8		—		—			4.8		—		3.5		1.3
Certificates of deposit		1.9		—		—			1.9		—		1.9		—
Subtotal		125.6		—		(0.3	)		125.3		3.5		71.4		50.4
Total	$	765.2	$	—	$	(0.4	)	$	764.8	$	618.7	$	86.1	$	60.0

(a)Valuations based on quoted prices for identical assets or 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.

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 March 31, 2022 and December 31, 2021 (in millions, except number of marketable debt securities in a loss position):

	March 31, 2022						December 31, 2021
	Fair Value of Marketable Debt Securities		Number of Marketable Debt Securities in a Loss Position		Unrealized Losses		Fair Value of Marketable Debt Securities		Number of Marketable Debt Securities in a Loss Position		Unrealized Losses
Corporate debt securities (c)	$	113.7		160	$	1.6	$	106.9		153	$	0.3
U.S. Treasury securities		22.6		25		0.1		22.4		27		0.1
U.S. government agency securities		5.5		7		0.3		4.8		6		—
Certificates of deposit		1.0		2		—		0.5		1		—
	$	142.8		194	$	2.0	$	134.6		187	$	0.4

(c)For 2022, includes one marketable debt security in a continuous loss position greater than 12 months with a fair value of $0.3 million and an insignificant amount of unrealized loss.