We invest surplus funds in excess of operational requirements in a diversified portfolio of marketable securities, with the objectives of delivering competitive returns, maintaining a high degree of liquidity, and seeking to avoid the permanent impairment of principal.

We regularly review our investment portfolio to identify and evaluate investments that have indicators of possible impairment. Investments are considered impaired when a decline in fair value is judged to be other-than-temporary. If the cost of an individual investment exceeds its fair value, we evaluate, among other factors, general market conditions, the duration and extent to which the fair value is less than cost, and our intent and ability to hold the investment. Once a decline in fair value is determined to be other-than-temporary, we will record an impairment charge and establish a new cost basis for the investment.

Marketable securities as of September 30, 2023 and December 31, 2022 consisted of the following (in thousands):

		September 30, 2023
		Cost or Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Marketable equity securities
Mutual funds	$	13,009	$	—	$	(1,381	)	$	11,628
Equity securities		69,253		3,087		(7,437	)		64,903
Total marketable equity securities		82,262		3,087		(8,818	)		76,531
Marketable debt securities
U.S. treasury securities		58,237		808		(87	)		58,958
Corporate bonds		16,123		273		(33	)		16,363
Total marketable debt securities		74,360		1,081		(120	)		75,321
	$	156,622	$	4,168	$	(8,938	)	$	151,852

		December 31, 2022
		Cost or Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Marketable equity securities
Mutual funds	$	26,352	$	—	$	(3,143	)	$	23,209
Equity securities		53,273		2,776		(5,836	)		50,213
Total marketable equity securities		79,625		2,776		(8,979	)		73,422
Marketable debt securities
U.S. treasury securities		25,640		182		(24	)		25,798
Corporate bonds		13,496		48		(106	)		13,438
Total marketable debt securities		39,136		230		(130	)		39,236
	$	118,761	$	3,006	$	(9,109	)	$	112,658

The amortized costs and fair value of our marketable debt securities, by contractual maturity, as of September 30, 2023 (in thousands) are as follows:

Our derivative instruments consisted of call and put options sold at their fair value as of the balance sheet date. These derivative instruments are reported as Other current liabilities on our Condensed Consolidated Balance Sheets as of September 30, 2023 and December 31, 2022 (in thousands):

		September 30, 2023
		Cost		Unrealized Losses		Fair Value
Derivative instruments	$	9,306	$	2,383	$	11,689
	$	9,306	$	2,383	$	11,689

		December 31, 2022
		Cost		Unrealized Losses		Fair Value
Derivative instruments	$	2,987	$	662	$	3,649
	$	2,987	$	662	$	3,649

A summary of realized and unrealized gains and losses from our equity securities and derivative instruments are as follows (in thousands):

		Three Months Ended September 30,						Nine Months Ended September 30,
		2023			2022			2023			2022
Net unrealized gains (losses) recognized on marketable equity securities	$	(287	)	$	(9,278	)	$	472		$	(14,062	)
Net realized gains (losses) recognized on marketable equity securities		(2,588	)		(555	)		3,643			218
Net unrealized gains (losses) recognized on derivative instruments		(1,631	)		3,907			(1,825	)		(696	)
Net realized gains recognized on derivative instruments		(72	)		2,214			2,165			4,089
Net realized gains recognized on marketable debt securities		—			188			217			556
Total net gains (losses) recognized in interest and other income (loss), net	$	(4,578	)	$	(3,524	)	$	4,672		$	(9,895	)

Our financial instruments measured at fair value on a recurring basis consisted of money-market funds, mutual funds, equity securities, corporate debt securities and derivatives. Equity securities are classified within Level 1 of the fair value hierarchy as they are valued based on quoted market price in an active market. Corporate debt securities and derivative instruments are valued based on quoted prices in markets that are less active, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency are generally classified within Level 2 of the fair value hierarchy.

Financial instruments valued based on unobservable inputs which reflect the reporting entity’s own assumptions or data that market participants would use in valuing an instrument are generally classified within Level 3 of the fair value hierarchy. We did not hold Level 3 financial instruments as of September 30, 2023, and December 31, 2022.

Financial instruments measured at fair value on a recurring basis as of September 30, 2023 and December 31, 2022 are classified based on the valuation technique in the table below (in thousands):

		September 30, 2023
		Fair Value Measurements Using
		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets:
U.S. treasury securities	$	58,958	$	—	$	—	$	58,958
Mutual funds		11,628		—		—		11,628
Equity securities		64,903		—		—		64,903
Corporate bonds		—		16,363		—		16,363
Total assets at fair value	$	135,489	$	16,363	$	—	$	151,852

Liabilities
Derivative instruments	$	—	$	11,689	$	—	$	11,689
Total liabilities at fair value	$	—	$	11,689	$	—	$	11,689

		December 31, 2022
		Fair Value Measurements Using
		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets:
Certificate of deposit	$	—	$	5,300	$	—	$	5,300
U.S. treasury securities		25,798		—		—		25,798
Mutual funds		23,209		—		—		23,209
Equity securities		50,213		—		—		50,213
Corporate bonds		—		13,438		—		13,438
Total assets at fair value	$	99,220	$	18,738	$	—	$	117,958

Liabilities
Derivative instruments	$	—	$	3,649	$	—	$	3,649
Total liabilities at fair value	$	—	$	3,649	$	—	$	3,649