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

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
June 30, 2019
U.S. government and federal agency securities	$	102,825	$	388	$	—		$	103,213
Certificates of deposit		8,748		67		—			8,815
Corporate bonds		249,377		1,070		(3	)		250,444
Equity securities		420		31,656		—			32,076
	$	361,370	$	33,181	$	(3	)	$	394,548

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2018
U.S. government and federal agency securities	$	103,410	$	93	$	(37	)	$	103,466
Certificates of deposit		8,992		—		—			8,992
Corporate bonds		282,902		36		(377	)		282,561
	$	395,304	$	129	$	(414	)	$	395,019

As of June 30, 2019 and December 31, 2018, 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 June 30, 2019 and December 31, 2018, the balance in the Company’s accumulated other comprehensive income (loss) consisted solely of net unrealized gains and losses on available-for-sale debt securities, net of income tax effects and reclassification adjustments for realized gains and losses. During the three and six months ended June 30, 2019, the Company recognized net unrealized gains on available-for-sale debt securities of $0.8 million and $1.8 million, respectively, and income tax expense of $0.3 million and $0.7 million, respectively, in other comprehensive income for the periods. The Company recognized net realized gains of zero and less than $0.1 million, respectively, on the sale or maturity of available-for-sale debt securities during the three and six months ended June 30, 2019, respectively, which were reclassified out of accumulated other comprehensive income (loss) during the periods and are included in investment income in the consolidated statements of operations and comprehensive income (loss). During the three and six months ended June 30, 2018, the Company recognized net unrealized gains (losses) on available-for-sale debt securities of $0.1 million and $(0.1) million, respectively, and income tax expense of zero in other comprehensive income (loss) for the periods. The Company did not recognize any realized gains or losses on the sale or maturity of available-for-sale debt securities during the three and six months ended June 30, 2018. Realized gains and losses from the sale or maturity of available-for-sale debt securities are determined based on the specific identification method.

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
June 30, 2019
Corporate bonds	$	19,176	$	(3	)	$	—	$	—	$	19,176	$	(3	)
	$	19,176	$	(3	)	$	—	$	—	$	19,176	$	(3	)

	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
December 31, 2018
U.S. government and federal agency securities	$	53,124	$	(37	)	$	—	$	—		$	53,124	$	(37	)
Corporate bonds		245,283		(354	)		12,424		(23	)		257,707		(377	)
	$	298,407	$	(391	)	$	12,424	$	(23	)	$	310,831	$	(414	)

As of June 30, 2019, available-for-sale debt securities held by the Company which were in an unrealized loss position consisted of 5 investment grade security positions. The Company has the intent and ability to hold such securities until recovery and has determined that none of the securities were other-than-temporarily impaired as of June 30, 2019 or December 31, 2018.

Marketable equity securities held by the Company as of June 30, 2019 consist solely of common stock of Prevail Therapeutics Inc. (Prevail). The Company acquired the securities as consideration for a commercial license to the NAV Technology Platform granted to Prevail in August 2017. Prevail completed its initial public offering (IPO) in June 2019. Prior to Prevail’s IPO, 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 are measured at fair value. The Company recorded an unrealized gain of $31.7 million during the three and six months ended June 30, 2019 related to the marketable equity securities of Prevail, which is included in investment income in the consolidated statements of operations and comprehensive income (loss). Pursuant to a lock-up agreement executed in connection with Prevail’s IPO, the Company is restricted from selling its common stock of Prevail prior to December 2019. As of June 30, 2019, no amounts have been realized by the Company related to its marketable securities of Prevail as there have been no sales of the securities.