3. Marketable Securities

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
June 30, 2018
U.S. government and federal agency securities	$	19,280	$	—	$	(14	)	$	19,266
Certificates of deposit		735		—		—			735
Corporate bonds		179,721		3		(325	)		179,399
	$	199,736	$	3	$	(339	)	$	199,400

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2017
Corporate bonds	$	130,018	$	2	$	(282	)	$	129,738
	$	130,018	$	2	$	(282	)	$	129,738

As of June 30, 2018 and December 31, 2017, no available-for-sale securities had remaining maturities greater than three years.

The amortized cost of available-for-sale securities is adjusted for amortization of premiums and accretion of discounts to maturity. As of June 30, 2018 and December 31, 2017, the balance in the Company’s accumulated other comprehensive loss consisted solely of net unrealized gains and losses on available-for-sale securities, net of income tax effects and reclassification adjustments for realized gains and losses. During the three months and six months ended June 30, 2018, the Company recognized net unrealized gains (losses) on available-for-sale securities of $0.1 million and $(0.1) million, respectively, and income tax expense of $0 in other comprehensive income (loss) for the period. The Company did not recognize any realized gains or losses on the sale or maturity of available-for-sale securities during the three and six months ended June 30, 2018. During the three and six months ended June 30, 2017, the Company recognized net unrealized losses on available-for-sale securities of $0.1 million and $0.1 million, respectively, and income tax expense of $0 in other comprehensive income (loss) for the period. The Company recognized net realized gains of $0 and $0.5 million on the sale or maturity of marketable securities during the three and six months ended June 30, 2017, respectively, which were reclassified out of accumulated other comprehensive loss during the period and are included in investment income in the consolidated statements of operations and comprehensive income (loss).

The following tables present the fair values and unrealized losses of marketable 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, 2018
U.S. government and federal agency securities	$	19,266	$	(14	)	$	—	$	—		$	19,266	$	(14	)
Corporate bonds		143,503		(239	)		21,066		(86	)		164,569		(325	)
	$	162,769	$	(253	)	$	21,066	$	(86	)	$	183,835	$	(339	)

	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
December 31, 2017
Corporate bonds	$	109,238	$	(180	)	$	17,124	$	(102	)	$	126,362	$	(282	)
	$	109,238	$	(180	)	$	17,124	$	(102	)	$	126,362	$	(282	)

As of June 30, 2018, securities held by the Company which were in an unrealized loss position consisted of 62 investment grade fixed income security positions. The Company has the intent and ability to hold such securities until recovery and has determined that none of its investments were other-than-temporarily impaired as of June 30, 2018 or December 31, 2017.