The following tables present a summary of the Company’s marketable securities, which consist solely of available-for-sale debt securities (in thousands):

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2021
U.S. government and agency securities	$	60,118	$	—	$	(229	)	$	59,889
Certificates of deposit		2,936		2		(11	)		2,927
Corporate bonds		442,792		62		(1,533	)		441,321
	$	505,846	$	64	$	(1,773	)	$	504,137

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2020
U.S. government and agency securities	$	12,782	$	22	$	—		$	12,804
Certificates of deposit		1,956		34		—			1,990
Corporate bonds		165,850		497		(55	)		166,292
Municipal securities		3,035		2		—			3,037
	$	183,623	$	555	$	(55	)	$	184,123

As of December 31, 2021 and 2020, no available-for-sale debt securities had remaining maturities greater than three years. The amortized cost of marketable debt securities is adjusted for amortization of premiums and accretion of discounts to maturity, or to the earliest call date for callable debt securities purchased at a premium.

As of December 31, 2021 and 2020, the balance in accumulated other comprehensive loss consisted solely of unrealized gains and losses on available-for-sale debt securities, net of reclassification adjustments for realized gains and losses and income tax effects. Unrealized gain (loss) on available-for-sale securities, net, presented in the statements of operations and comprehensive income (loss) consisted of the following (in thousands):

	Years Ended December 31,
	2021			2020			2019
Unrealized gain (loss) before reclassifications	$	(2,202	)	$	(426	)	$	1,392
Realized gains reclassified to investment income		(7	)		(139	)		(40	)
Income tax expense		—			—			(467	)
Unrealized gain (loss) on available-for-sale securities, net	$	(2,209	)	$	(565	)	$	885

The following tables present the fair values and unrealized losses of available-for-sale debt securities held by the Company in an unrealized loss position for less than 12 months and 12 months or greater (in thousands):

	Less than 12 Months					12 Months or Greater				Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
December 31, 2021
U.S. government and agency securities	$	59,889	$	(229	)	$	—	$	—	$	59,889	$	(229	)
Certificates of deposit		2,195		(11	)		—		—		2,195		(11	)
Corporate bonds		385,115		(1,533	)		—		—		385,115		(1,533	)
	$	447,199	$	(1,773	)	$	—	$	—	$	447,199	$	(1,773	)

	Less than 12 Months					12 Months or Greater				Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
December 31, 2020
Corporate bonds	$	55,507	$	(55	)	$	—	$	—	$	55,507	$	(55	)
	$	55,507	$	(55	)	$	—	$	—	$	55,507	$	(55	)

As of December 31, 2021, available-for-sale debt securities held by the Company which were in an unrealized loss position consisted of 92 investment grade security positions. The Company has the intent and ability to hold such securities until recovery, and based on the credit quality of the issuers and low severity of each unrealized loss position relative to its amortized cost basis, the Company did not identify any credit losses associated with its available-for-sale debt securities. The Company did not recognize any impairment or credit losses on available-for-sale debt securities during the years ended December 31, 2021, 2020 and 2019.

During the years ended December 31, 2020 and 2019, the Company recognized total net realized and unrealized gains of $4.8 million and $37.8 million, respectively, related to its marketable equity securities of Prevail Therapeutics Inc. (Prevail). The Prevail securities were acquired as consideration for a license to the NAV Technology Platform granted to Prevail in August 2017. Prevail completed its initial public offering (IPO) in June 2019, prior to which the securities were accounted for as non-marketable equity securities without a readily determinable fair value and had a carrying value of $0.4 million. Upon Prevail’s IPO in June 2019, the securities were reclassified to marketable securities and remeasured at fair value at each subsequent reporting date. As of December 31, 2020, the Company had sold all of its Prevail equity securities.