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 three-tier fair value hierarchy:


	December 31, 2022
	Total		Level 1		Level 2		Level 3
	(in thousands)
Equity securities, debt securities and cash equivalents:
U.S. government debt securities	$	332,048	$	—	$	332,048	$	—
Corporate debt securities		194,149		—		194,149		—
U.S. agency debt securities		156,688		—		156,688		—
U.S. treasury bills		69,798		69,798		—		—
Money market accounts		27,455		27,455		—		—
Municipal bonds		22,673		—		22,673		—
Preferred stock of privately held company		15,000		—		—		15,000
Redeemable preferred stock investment		12,385		—		—		12,385
Yankee debt securities		3,010		—		3,010		—
Total equity securities, debt securities and cash equivalents	$	833,206	$	97,253	$	708,568	$	27,385


	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 U.S. treasury bills, money market instruments, bond funds, and exchange traded funds 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 December 31, 2022, the Company had preferred stock of a privately held company, which was included in other long-term assets in the accompanying Consolidated Balance Sheets, and

redeemable preferred stock of a private company that were measured using unobservable (Level 3) inputs. The fair value of redeemable preferred stock as of December 31, 2022 and 2021 was based on 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 preferred stock of the privately held company did not have a readily determinable fair value, and no impairment loss was recorded as of December 31, 2022.

There were no transfers between fair value measurement levels in 2022, 2021, and 2020.