Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

The following is a summary of marketable securities at December 31, 2017 and December 31, 2016 (in thousands):



	December 31, 2017
	Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Values
Available-for-sale securities
Corporate bonds and notes	$	45,803	$	—	$	(230	)	$	45,573
Commercial paper	2,392		—		(2		)	2,390
Treasury and agency notes and bills	6,000		—		(71		)	5,929
Certificates of deposit	8,540		—		—			8,540
Money market funds	40,413		—		—			40,413
Total available-for-sale securities	$	103,148	$	—	$	(303	)	$	102,845
Reported in:
Cash and cash equivalents								$	40,413
Short-term investments								62,432
Total marketable securities								$	102,845



	December 31, 2016
	Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Values
Available-for-sale securities
Corporate bonds and notes	$	36,590	$	7	$	(95	)	$	36,502
Commercial paper	5,220		—		(4		)	5,216
Treasury and agency notes and bills	6,029		—		(57		)	5,972
Money market funds	14,146		—		—			14,146
Total available-for-sale securities	$	61,985	$	7	$	(156	)	$	61,836
Reported in:
Cash and cash equivalents								$	14,457
Short-term investments								47,379
Total marketable securities								$	61,836

Schedule of Gross Unrealized Losses on Investments

The following table summarizes the fair value and gross unrealized losses related to individual available-for-sale securities at December 31, 2017 and 2016, which have been in a continuous unrealized loss position, aggregated by investment category and length of time (in thousands):



December 31, 2017	Less Than 12 Months					12 Months or More					Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Corporate bonds and notes	$	30,811	$	(189	)	$	14,762	$	(41	)	$	45,573	$	(230	)
Treasury and agency notes and bills	—		—			5,929		(71		)	5,929		(71		)
Commercial paper	2,390		(2		)	—		—			2,390		(2		)
Total	$	33,201	$	(191	)	$	20,691	$	(112	)	$	53,892	$	(303	)



December 31, 2016	Less Than 12 Months					12 Months or More					Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Corporate bonds and notes	$	14,678	$	(44	)	$	13,230	$	(51	)	$	27,908	$	(95	)
Treasury and agency notes and bills	5,972		(57		)	—		—			5,972		(57		)
Commercial paper	5,216		(4		)	—		—			5,216		(4		)
Total	$	25,866	$	(105	)	$	13,230	$	(51	)	$	39,096	$	(156	)

Estimated Fair Value of Marketable Securities by Contractual Maturity

The estimated fair value of marketable securities by contractual maturity at December 31, 2017 is shown below (in thousands). Actual maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations without call or prepayment penalties.



	Estimated Fair Value
Due in one year or less	$	73,889
Due in one to two years	19,180
Due in two to three years	9,776
Total	$	102,845