Financial Instruments

12 Months Ended

Dec. 31, 2018

Investments Debt And Equity Securities [Abstract]

Financial Instruments

5. Financial Instruments

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

	December 31, 2018									December 31, 2017
								Estimated									Estimated
	Amortized		Unrealized		Unrealized			Fair		Amortized		Unrealized		Unrealized			Fair
	Cost		Gain		(Loss)			Value		Cost		Gain		(Loss)			Value
Money market funds	$	19,500	$	—	$	—		$	19,500	$	31,836	$	—	$	—		$	31,836
Corporate notes and commercial paper		166,363		1		(205	)		166,159		313,307		2		(145	)		313,164
U.S. Treasury bills and government agency securities		110,270		1		(81	)		110,190		170,724		—		(266	)		170,458
	$	296,133	$	2	$	(286	)	$	295,849	$	515,867	$	2	$	(411	)	$	515,458
Classified as:
Cash equivalents								$	117,836								$	162,793
Short-term investments									178,013									281,589
Long-term investments									—									71,076
Total cash equivalents and investments								$	295,849								$	515,458

At December 31, 2018, the remaining contractual maturities of available-for-sale securities were less than one year. There have been no significant realized losses on available-for-sale securities for the periods presented. We do not intend to sell the investments with unrealized losses at December 31, 2018, and it is not more likely than not that we will be required to sell those investments with unrealized losses before recovery of their amortized cost bases, which may be maturity. Available-for-sale debt securities that were in a continuous loss position but were not deemed to be other than temporarily impaired were immaterial at both December 31, 2018 and 2017.