Financial Instruments

9 Months Ended

Sep. 30, 2018

Investments Debt And Equity Securities [Abstract]

Financial Instruments

5. Financial Instruments

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

	September 30, 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	$	15,062	$	—	$	—		$	15,062	$	31,836	$	—	$	—		$	31,836
Corporate notes and commercial paper		200,666		3		(238	)		200,431		313,307		2		(145	)		313,164
U.S. Treasury bills and government agency securities		148,837		—		(201	)		148,636		170,724		—		(266	)		170,458
	$	364,565	$	3	$	(439	)	$	364,129	$	515,867	$	2	$	(411	)	$	515,458
Classified as:
Cash equivalents								$	129,964								$	162,793
Short-term investments									223,284									281,589
Long-term investments									10,881									71,076
Total cash equivalents and investments								$	364,129								$	515,458

At September 30, 2018, the remaining contractual maturities of available-for-sale securities were less than two years. 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 September 30, 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 September 30, 2018 and December 31, 2017.