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 June 30, 2023 and December 31, 2022 consisted of the following (in thousands):

		June 30, 2023
		Cost or Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Marketable equity securities
Mutual funds	$	27,020	$	—	$	(2,955	)	$	24,065
Equity securities		67,800		3,214		(5,703	)		65,311
Total marketable equity securities		94,820		3,214		(8,658	)		89,376
Marketable debt securities
U.S. treasury securities		48,534		807		(43	)		49,298
Corporate bonds		13,305		87		(99	)		13,293
Total marketable debt securities		61,839		894		(142	)		62,591
	$	156,659	$	4,108	$	(8,800	)	$	151,967

		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 June 30, 2023 (in thousands) are as follows:

		June 30, 2023
		Amortized Cost		Fair Value
Less than 1 year	$	41,559	$	42,342
1 to 5 years		20,280		20,249
More than 5 years		—		—
Total	$	61,839	$	62,591

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

		June 30, 2023
		Cost		Unrealized Losses		Fair Value
Derivative instruments	$	5,471	$	752	$	6,223
	$	5,471	$	752	$	6,223

		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 June 30,						Six Months Ended June 30,
		2023			2022			2023			2022
Net unrealized gains (losses) recognized on marketable equity securities	$	(1,255	)	$	(6,923	)	$	759		$	(4,784	)
Net realized gains (losses) recognized on marketable equity securities		4,561			(254	)		6,230			772
Net unrealized losses recognized on derivative instruments		(91	)		(1,943	)		(194	)		(4,603	)
Net realized gains recognized on derivative instruments		1,520			2,009			2,237			1,875
Net realized gains recognized on marketable debt securities		217			—			217			368
Total net gains (losses) recognized in interest and other income (loss), net	$	4,952		$	(7,111	)	$	9,249		$	(6,372	)

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 June 30, 2023, and December 31, 2022.

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

		June 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	$	49,298	$	—	$	—	$	49,298
Mutual funds		24,065		—		—		24,065
Equity securities		65,311		—		—		65,311
Corporate bonds		—		13,293		—		13,293
Total assets at fair value	$	138,674	$	13,293	$	—	$	151,967

Liabilities
Derivative instruments	$	—	$	6,223	$	—	$	6,223
Total liabilities at fair value	$	—	$	6,223	$	—	$	6,223

		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