Marketable Securities

12 Months Ended

Dec. 31, 2016

Investments Debt And Equity Securities [Abstract]

Marketable Securities

3. Marketable Securities

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

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2016
Corporate bonds	$	133,424	$	82	$	(298	)	$	133,208
Common equity securities		300		618		—			918
	$	133,724	$	700	$	(298	)	$	134,126

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2015
Corporate bonds	$	157,977	$	4	$	(759	)	$	157,222
Commercial paper		4,990		—		—			4,990
Common equity securities		3		36		—			39
	$	162,970	$	40	$	(759	)	$	162,251

As of December 31, 2015, the Company’s common equity securities consisted of shares of common stock of Dimension Therapeutics, Inc. (Dimension), which became a publicly traded company in October 2015. The Company obtained these shares in connection with a license granted to Dimension in October 2013. As of December 31, 2016, the Company had sold all of its shares of Dimension common stock.

As of December 31, 2016, the Company’s common equity securities consisted of shares of common stock of Audentes, which became a publicly traded company in July 2016. The Company obtained these shares in connection with a license granted to Audentes in July 2013. The Company was restricted from trading these securities until January 2017 pursuant to a lock-up agreement entered into in connection with Audentes’ IPO. The Company has classified these shares as available-for-sale securities and recognized an unrealized gain of $0.6 million, which is included in accumulated other comprehensive loss as of December 31, 2016. Prior to Audentes’ IPO, the shares were not marketable and were accounted for as a cost method investment on the Company’s balance sheets.

As of December 31, 2016 and 2015, 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 December 31, 2016 and 2015, 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. For the years ended December 31, 2016, 2015 and 2014, the Company recognized net unrealized gains (losses) on available-for-sale securities of $1.1 million, $(0.7) million and $0, respectively, and income tax expense of $0.4 million, $0 and $0, respectively, in other comprehensive income (loss). The Company recognized net realized losses of less than $0.1 million on the sale or maturity of available-for-sale securities during the year ended December 31, 2016, which were reclassified out of accumulated other comprehensive loss during the period. The Company did not recognize any realized gains or losses on the sale or maturity of available-for-sale securities during the years ended December 31, 2015 or 2014.

The Company did not hold any securities in an unrealized loss position for more than twelve months as of December 31, 2016 or 2015. The aggregate fair value of securities held by the Company in an unrealized loss position for less than twelve months as of December 31, 2016 and 2015 was $102.5 million and $155.5 million, respectively. As of December 31, 2016, securities held by the Company which were in an unrealized loss position consisted of thirty-four investment grade corporate bond 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 December 31, 2016 or 2015.