Financial Instruments

12 Months Ended

Dec. 31, 2017

Investments All Other Investments [Abstract]

Financial Instruments

4. Financial Instruments

Cash equivalents, restricted cash and short-term investments which are classified as available-for-sale securities, consisted of the following (in thousands):

December 31, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds	$	14,334	$	—	$	—		$	14,334
U.S. government agency securities		16,474		—		(3	)		16,471
Restricted cash (money market funds)		5,330		3		—			5,333
Agency securities		1,500		—		—			1,500
Total financial assets	$	37,638	$	3	$	(3	)	$	37,638
Classified as:
Cash and cash equivalents								$	14,334
Short-term investments									17,971
Restricted cash (money market funds)									5,333
								$	37,638

December 31, 2016	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds	$	10,156	$	—	$	—		$	10,156
U.S. government agency securities		6,802		—		(2	)		6,800
Restricted cash (money market funds)		19,593		—		—			19,593
Total financial assets	$	36,551	$	—	$	(2	)	$	36,549
Classified as:
Cash and cash equivalents								$	10,156
Restricted cash (money market funds)									19,593
Short-term investments									6,800
								$	36,549

As of December 31, 2017, the remaining contractual maturities of available-for-sale securities was less than one year. There have been no material realized gains or losses on available-for-sale securities for the periods presented. The carrying amounts of cash, accounts receivable, other receivables, accounts payable, other payables and redeemable convertible notes approximate their fair values due to the short-term maturity of these instruments.