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

		March 31, 2023
		Cost or Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Marketable equity securities
Mutual funds	$	26,683	$	—	$	(2,988	)	$	23,695
Equity securities		56,485		4,877		(6,077	)		55,285
Total marketable equity securities		83,168		4,877		(9,065	)		78,980
Marketable debt securities
U.S. treasury securities		48,534		413		(13	)		48,934
Corporate bonds		18,555		211		(156	)		18,610
Total marketable debt securities		67,089		624		(169	)		67,544
	$	150,257	$	5,501	$	(9,234	)	$	146,524

		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 March 31, 2023 (in thousands) are as follows:

		March 31, 2023
		Amortized Cost		Fair Value
Less than 1 year	$	41,559	$	41,939
1 to 5 years		20,247		20,204
More than 5 years		5,283		5,400
Total	$	67,089	$	67,543

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 March 31, 2023 and December 31, 2022 (in thousands):

		March 31, 2023
		Cost		Unrealized Losses		Fair Value
Derivative instruments	$	6,848	$	662	$	7,510
	$	6,848	$	662	$	7,510

		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 March 31,
		2023			2022
Net unrealized gains recognized on marketable equity securities	$	2,014		$	2,140
Net realized gains recognized on marketable equity securities		1,669			1,026
Net unrealized losses recognized on derivative instruments		(102	)		(2,661	)
Net realized gains (losses) recognized on derivative instruments		717			(134	)
Net realized gains recognized on marketable debt securities		—			368
Total net gains recognized in interest and other income (loss), net	$	4,298		$	739

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 March 31, 2023, and December 31, 2022.

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

		March 31, 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	$	—	$	48,934	$	—	$	48,934
Mutual funds		23,695		—		—		23,695
Equity securities		55,285		—		—		55,285
Corporate bonds		—		18,610		—		18,610
Total assets at fair value	$	78,980	$	67,544	$	—	$	146,524

Liabilities
Derivative instruments	$	—	$	7,510	$	—	$	7,510
Total liabilities at fair value	$	—	$	7,510	$	—	$	7,510

		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	$	73,422	$	44,536	$	—	$	117,958

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