Financial Instruments

6 Months Ended

Jun. 30, 2018

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):

June 30, 2018	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds (cash equivalents)	$	45,949	$	—	$	—		$	45,949
U.S. government agency securities		89,609		5		(1	)		89,613
Restricted cash (money market funds)		175		—		—			175
Total financial assets	$	135,733	$	5	$	(1	)	$	135,737
Classified as:
Cash and cash equivalents								$	45,949
Short-term investments									89,613
Restricted cash (money market funds)									175
								$	135,737

December 31, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Money market funds (cash equivalents)	$	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

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.