5. Cash, Money Market Funds and Marketable Securities

As of December 31, 2017, the Company held $49.1 million in cash and cash equivalents and $309.5 million of available-for-sale securities which are reported at fair value on the Company's Consolidated Balance Sheets. Unrealized gains and losses are reported within accumulated other comprehensive income/ (loss) in the statements of comprehensive loss. If a decline in the fair value of a marketable security below the Company's cost basis is determined to be other than temporary, such marketable security is written down to its estimated fair value as a new cost basis and the amount of the write-down is included in earnings as an impairment charge. To date, only temporary impairment adjustments have been recorded.

The Company regularly invests excess operating cash in deposits with major financial institutions, money market funds, notes issued by the U.S. government, as well as fixed income investments and U.S. bond funds both of which can be readily purchased and sold using established markets. The Company believes that the market risk arising from its holdings of these financial instruments is mitigated as many of these securities are either government backed or of the highest credit rating. Investments that have original maturities or greater than 3 months but less than 1 year are classified as short-term and investments with maturities that are greater than 1 year are classified as long-term. As of December 31, 2017, all the investments were classified as short-term on the Company's Consolidated Balance Sheets.

The Company transacts business in various foreign countries and therefore, is subject to risk of foreign currency exchange rate fluctuations. As such, in June 2016 the Company entered into a forward contract to economically hedge transactional exposure associated with commitments arising from trade accounts payable denominated in a currency other than the functional currency of the respective operating entity. The Company does not designate these forward contracts as hedging instruments under applicable accounting guidance and, therefore, changes in fair value are recorded within other income (expense) in the Consolidated Statements of Operations, with the corresponding liability in current liabilities on the Consolidated Balance Sheet. For the years ended December 31, 2017 and 2016, we recognized a loss of $0.2 million and $0.3 million, respectively, related to the foreign currency forward contract not designated as hedging instruments in other expense in the Consolidated Statements of Operations. For the year ended December 31, 2016, the Company also recognized a corresponding liability of $0.3 million as other current liability in the Consolidated Balance Sheets. As the forward contract settled in June 2017, there was no liability for the year ended December 31, 2017.

Cash and available for sale securities consisted of the following as of December 31, 2017 and December 31, 2016 (in thousands):

	As of December 31, 2017
	Cost		Unrealized Gain		Unrealized Loss			Fair Value
Cash balances	$	49,060	$	—	$	—		$	49,060
Corporate debt securities, current portion		199,314		1		(303	)		199,012
Commercial paper		79,878		—		(75	)		79,803
Asset-backed securities		30,346		—		(59	)		30,287
Money market		350		—		—			350
Certificate of deposit		50		—		—			50

	$	358,998	$	1	$	(437	)	$	358,562


Included in cash and cash equivalents	$	49,060	$	—	$	—		$	49,060
Included in marketable securities		309,938		1		(437	)		309,502

Total cash and marketable securities	$	358,998	$	1	$	(437	)	$	358,562

	As of December 31, 2016
	Cost		Unrealized Gain		Unrealized Loss			Fair Value
Cash balances	$	187,026	$	—	$	—		$	187,026
Corporate debt securities, current portion		74,564		2		(31	)		74,535
Commercial paper		68,258		132		—			68,390
Money market		350		—		—			350
Certificate of deposit		50		—		—			50

	$	330,248	$	134	$	(31	)	$	330,351


Included in cash and cash equivalents	$	187,026	$	—	$	—		$	187,026
Included in marketable securities		143,222		134		(31	)		143,325

Total cash and marketable securities	$	330,248	$	134	$	(31	)	$	330,351

For the years ended December 31, 2017 and 2016, there were no realized gains or losses. The cost of securities sold is based on the specific identification method.

Unrealized loss positions in the available for sale securities as of December 31, 2017 and December 31, 2016 reflect temporary impairments that have been in a loss position for less than twelve months and as such are recognized in other comprehensive gain/ (loss). The fair value of these available for sale securities in unrealized loss positions was $295.1 million and $58.7 million as of December 31, 2017 and 2016, respectively.

The Company holds available-for-sale investment securities which are reported at fair value on the Company's balance sheet. Unrealized gains and losses are reported within accumulated other comprehensive income ("AOCI") in the statements of comprehensive loss.