Available-for-sale debt securities are recorded at fair value, with the portion of the unrealized gains and losses that are not credit-related included as a component of accumulated other comprehensive loss in stockholders’ equity, until realized. Available-for-sale debt securities consisted of the following (in millions):


As of March 31, 2025	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
U.S. government and agency securities	$	2,681.0	$	6.8	$	(1.1)	$	2,686.7
Corporate debt securities	586.8		2.5		(0.1)		589.2

Total	$	3,267.8	$	9.3	$	(1.2)	$	3,275.9


Reported under the following captions in our consolidated balance sheets:
Cash and cash equivalents	$	162.4
Current marketable investments	1,402.8
Non-current marketable investments	1,710.7
Total	$	3,275.9


As of December 31, 2024	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
U.S. government and agency securities	$	2,473.7	$	3.1	$	(3.5)	$	2,473.3
Corporate debt securities	568.0		1.9		(0.5)		569.4

Total	$	3,041.7	$	5.0	$	(4.0)	$	3,042.7


Reported under the following captions in our consolidated balance sheets:
Cash and cash equivalents	$	21.5
Current marketable investments	1,545.9
Non-current marketable investments	1,475.3
Total	$	3,042.7

The following tables present gross unrealized losses and fair value for those available-for-sale debt securities that were in an unrealized loss position as of March 31, 2025 and December 31, 2024, aggregated by investment category and length of time that the individual securities have been in a continuous loss position (in millions):


	Less than 12 months				12 months or longer				Total
As of March 31, 2025	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
U.S. government and agency securities	$	708.6	$	(1.0)	$	146.5	$	(0.1)	$	855.1	$	(1.1)
Corporate debt securities	48.9		(0.1)		22.0		—		70.9		(0.1)
Total	$	757.5	$	(1.1)	$	168.5	$	(0.1)	$	926.0	$	(1.2)


	Less than 12 months				12 months or longer				Total
As of December 31, 2024	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
U.S. government and agency securities	$	947.3	$	(3.3)	$	341.1	$	(0.2)	$	1,288.4	$	(3.5)
Corporate debt securities	75.0		(0.2)		82.0		(0.3)		157.0		(0.5)
Total	$	1,022.3	$	(3.5)	$	423.1	$	(0.5)	$	1,445.4	$	(4.0)

As of March 31, 2025 and December 31, 2024, we held 181 and 227 available-for-sale debt securities, respectively, that were in an unrealized loss position. In assessing whether the decline in fair value as of March 31, 2025 of any of these securities resulted from a credit loss, we consulted with our investment managers and reviewed the credit ratings for each security. We believe that these unrealized losses are a direct result of the current interest rate environment and do not represent an indication of credit loss. We do not intend to sell the investments in unrealized loss positions prior to their maturity and it is not more likely than not that we will be required to sell these investments before recovery of their amortized cost basis. There were no impairments due to credit loss on our available-for-sale debt securities during the three months ended March 31, 2025 and 2024.

During the first quarter of 2024, we sold certain available-for-sale debt securities prior to maturity to fund the repurchase of our common stock. See Note 9—Stockholders’ Equity—Share Repurchase for further information. As a result of the sale, we received $831.8 million in proceeds and recognized gross realized gains of $0.4 million and gross realized losses of $1.8 million. The net realized loss of $1.4 million is included in other (expense) income, net in our consolidated statements of operations.

The following table summarizes the contractual maturities of available-for-sale debt securities (in millions). Actual maturities may differ from contractual maturities because the issuers of certain of these debt securities have the right to call the securities or prepay their obligations under the securities with or without penalties.

We held investments in equity securities with readily determinable fair values, in the aggregate, of $18.6 million and $23.9 million as of March 31, 2025 and December 31, 2024, respectively, which are included in current marketable investments in our consolidated balance sheets. Changes in the fair value of publicly-traded equity securities are recorded in our consolidated statements of operations within other (expense) income, net. See Note 4—Fair Value Measurements.

As of March 31, 2025 and December 31, 2024, we maintained non-controlling equity investments in privately-held companies of $59.0 million in the aggregate. We measure these investments using the measurement alternative because the fair values of these investments are not readily determinable. Under this alternative, the investments are measured at cost, less any impairment, and adjusted for any observable price changes. We include our investments in privately-held companies within other non-current assets in our consolidated balance sheets. These investments are subject to a periodic impairment review and, if impaired, the investment is measured and recorded at fair value in accordance with ASC 820, Fair Value Measurements.