The authoritative guidance on fair value measurements establishes a framework with respect to measuring assets and liabilities at fair value on a recurring basis and non-recurring basis. Under the framework, fair value is defined as the exit price, or the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants, as of the measurement date. The framework also establishes a three-tier hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs market participants would use in valuing the asset or liability and are developed based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the factors market participants would use in valuing the asset or liability and are developed based on the best information available in the circumstances. The hierarchy consists of the following three levels:

The following tables present information about the Company’s financial assets measured at fair value on a recurring basis, based on the above three-tier fair value hierarchy:


	June 30, 2022
	Total		Level 1		Level 2		Level 3
	(in thousands)
Equity securities, debt securities and cash equivalents:
Investment in private equity securities	$	15,000	$	—	$	—	$	15,000
U.S. government debt securities		357,573		—		357,573		—
Corporate debt securities		257,716		—		257,716		—
U.S. agency debt securities		81,832		—		81,832		—
Municipal bonds		24,060		—		24,060		—
Yankee debt securities		11,801		—		11,801		—
U.S. treasury bills		59,261		59,261		—		—
Money market accounts		44,209		44,209		—		—
Redeemable preferred stock investment		11,981		—		—		11,981
Total equity securities, debt securities and cash equivalents	$	863,433	$	103,470	$	732,982	$	26,981


	December 31, 2021
	Total		Level 1		Level 2		Level 3
	(in thousands)
Equity securities, debt securities and cash equivalents:
Corporate debt securities	$	332,529	$	—	$	332,529	$	—
U.S. government debt securities		198,157		—		198,157		—
Bond funds		98,799		98,799		—		—
U.S. agency debt securities		69,534		—		69,534		—
Exchange traded funds		35,000		35,000		—		—
Municipal bonds		24,480		—		24,480		—
Yankee debt securities		12,153		—		12,153		—
Redeemable preferred stock investment		21,965		—		—		21,965
Money market accounts		77,067		77,067		—		—
Total equity securities, debt securities and cash equivalents	$	869,684	$	210,866	$	636,853	$	21,965

The Company’s Level 1 assets include bond funds, exchange traded funds, U.S. treasury bills, and money market instruments and are valued based upon observable market prices. Level 2 assets consist of U.S. government and U.S. agency debt securities, municipal bonds, corporate debt securities and Yankee debt securities. Level 2 securities are valued based upon observable inputs that include reported trades, broker/dealer quotes, bids and offers. As of June 30, 2022, the Company had $15.0 million of investment in private equity securities, which was included in other long-term assets in the accompanying Condensed Consolidated Balance Sheets, and $12.0 million of redeemable preferred stock of a private company that were measured using unobservable (Level 3) inputs. The fair values of redeemable preferred stock as of June 30, 2022 and December 31, 2021 were based on the valuation performed by a third-party valuation company utilizing the guideline public company method under market approach and the discounted cash flow method under income approach. For the value of the investment in private equity securities, the Company elected to measure it at cost minus impairment as the private equity securities did not have a readily determinable fair value, and the Company did not believe the investment was impaired as of June 30, 2022.

There were no transfers between fair value measurement levels during the three and six months ended June 30, 2022.