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

6 Months Ended

Jun. 30, 2023

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 June 30, 2023 and December 31, 2022 (in millions):

	June 30, 2023
	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	$	474.4	$	—	$	—		$	474.4	$	474.4	$	—	$	—
Level 1 (a):
U.S. Treasury securities		30.0		—		(0.4	)		29.6		—		16.6		13.0
Money market funds		1.7		—		—			1.7		1.7		—		—
Subtotal		31.7		—		(0.4	)		31.3		1.7		16.6		13.0
Level 2 (b):
Corporate debt securities		107.6		—		(1.4	)		106.2		—		73.9		32.3
U.S. government agency securities		11.8		—		(0.1	)		11.7		—		6.4		5.3
Certificates of deposit		6.0		—		—			6.0		1.0		5.0		—
Subtotal		125.4		—		(1.5	)		123.9		1.0		85.3		37.6
Total	$	631.5	$	—	$	(1.9	)	$	629.6	$	477.1	$	101.9	$	50.6

	December 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	$	318.3	$	—	$	—		$	318.3	$	318.3	$	—	$	—
Level 1 (a):
U.S. Treasury securities		24.3		—		(0.4	)		23.9		—		16.7		7.2
Money market funds		0.1		—		—			0.1		0.1		—		—
Subtotal		24.4		—		(0.4	)		24.0		0.1		16.7		7.2
Level 2 (b):
Corporate debt securities		123.9		—		(2.1	)		121.8		1.6		65.7		54.5
U.S. government agency securities		4.5		—		(0.1	)		4.4		—		1.2		3.2
Certificates of deposit		1.6		—		—			1.6		—		1.6		—
Subtotal		130.0		—		(2.2	)		127.8		1.6		68.5		57.7
Total	$	472.7	$	—	$	(2.6	)	$	470.1	$	320.0	$	85.2	$	64.9

(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 tables provide information about the Company’s marketable debt securities that have been in a continuous loss position as of June 30, 2023 and December 31, 2022 (in millions, except number of marketable debt securities in a loss position):

	June 30, 2023
	Fair Value of Marketable Debt Securities in a Loss Position < 12 Months		Number of Marketable Debt Securities in a Loss Position < 12 Months		Unrealized Losses < 12 Months		Fair Value of Marketable Debt Securities in a Loss Position ≥ 12 Months		Number of Marketable Debt Securities in a Loss Position ≥ 12 Months		Unrealized Losses ≥ 12 Months
Corporate debt securities	$	62.9		76	$	0.5	$	35.9		48	$	0.9
U.S. Treasury securities		20.6		20		0.2		9.0		12		0.2
U.S. government agency securities		10.9		18		0.1		0.8		1		—
Certificates of deposit		2.1		3		—		—		—		—
	$	96.5		117	$	0.8	$	45.7		61	$	1.1

	December 31, 2022
	Fair Value of Marketable Debt Securities in a Loss Position < 12 Months		Number of Marketable Debt Securities in a Loss Position < 12 Months		Unrealized Losses < 12 Months		Fair Value of Marketable Debt Securities in a Loss Position ≥ 12 Months		Number of Marketable Debt Securities in a Loss Position ≥ 12 Months		Unrealized Losses ≥ 12 Months
Corporate debt securities	$	77.0		113	$	1.0	$	37.9		50	$	1.1
U.S. Treasury securities		14.5		14		0.2		9.3		13		0.3
U.S. government agency securities		3.2		5		—		1.3		3		—
	$	94.7		132	$	1.2	$	48.5		66	$	1.4