Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2018

Investments, Debt and Equity Securities [Abstract]

The following is a summary of marketable securities at June 30, 2018 and December 31, 2017 (in thousands):



	June 30, 2018
	Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Values
Available-for-sale securities
Corporate bonds and notes	$	33,905	$	—	$	(377	)	$	33,528
Treasury and agency notes and bills	6,000		—		(79		)	5,921
Money market funds	8,781		—		—			8,781
Total available-for-sale securities	$	48,686	$	—	$	(456	)	$	48,230
Reported in:
Cash and cash equivalents								$	8,781
Short-term investments								39,449
Total marketable securities								$	48,230



	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

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 June 30, 2018 and December 31, 2017, which have been in a continuous unrealized loss position, aggregated by investment category and length of time (in thousands):



June 30, 2018	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	$	24,340	$	(325	)	$	9,188	$	(52	)	$	33,528	$	(377	)
Treasury and agency notes and bills	—		—			5,921		(79		)	5,921		(79		)
Total	$	24,340	$	(325	)	$	15,109	$	(131	)	$	39,449	$	(456	)



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	)
Commercial paper	2,390		(2		)	—		—			2,390		(2		)
Treasury and agency notes and bills	—		—			5,929		(71		)	5,929		(71		)
Total	$	33,201	$	(191	)	$	20,691	$	(112	)	$	53,892	$	(303	)

Estimated Fair Value of Marketable Securities by Contractual Maturity

The estimated fair value of marketable securities by contractual maturity at June 30, 2018 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	$	23,954
Due in one to two years	22,315
Due in two to three years	1,961
Total	$	48,230