Available-for-Sale Marketable Securities

12 Months Ended

Dec. 31, 2020

Investments Debt And Equity Securities [Abstract]

Available-for-Sale Marketable Securities

3. Available-for-Sale Marketable Securities

As of December 31, 2020 and 2019, the Company’s available-for-sale marketable securities consisted of debt securities issued by the U.S. Treasury, U.S. government-sponsored entities and investment grade institutions as well as municipal bonds.

The following tables summarize the Company’s available-for-sale marketable securities by major type of security as of December 31, 2020 and 2019:

As of December 31, 2020

			Gross Unrealized				Estimated Fair
Type of Security	Amortized Cost		Gains		Losses		Value
U.S. Treasury securities	$	20,710	$	41	$	(1)	$	20,750
U.S. government agency obligations		22,125		4		(1)		22,128
Corporate bonds		49,080		61		(23)		49,118
Commercial paper		116,139		5		(17)		116,127
Municipal bonds		11,680		12		(8)		11,684
Total available-for-sale marketable securities	$	219,734	$	123	$	(50)	$	219,807

As of December 31, 2019

			Gross Unrealized				Estimated Fair
Type of Security	Amortized Cost		Gains		Losses		Value
U.S. Treasury securities	$	16,052	$	31	$	(2)	$	16,081
U.S. government agency obligations		25,803		14		(1)		25,816
Corporate bonds		115,788		125		(23)		115,890
Commercial paper		38,547		27		(1)		38,573
Municipal bonds		3,500		—		—		3,500
Total available-for-sale marketable securities	$	199,690	$	197	$	(27)	$	199,860

The following tables summarize the fair value and gross unrealized losses of the Company’s available-for-sale marketable securities by investment category and disaggregated by the length of time that individual debt securities have been in a continuous unrealized loss position as of December 31, 2020 and 2019:

As of December 31, 2020

	Less than 12 Months				12 Months or Greater				Total
			Gross				Gross				Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
	Value		Losses		Value		Losses		Value		Losses
U.S. Treasury securities	$	12,682	$	(1)	$	—	$	—	$	12,682	$	(1)
U.S. government agency obligations		2,500		(1)		—		—		2,500		(1)
Corporate bonds		23,553		(23)		—		—		23,553		(23)
Commercial paper		68,897		(17)		—		—		68,897		(17)
Municipal bonds		6,259		(8)		—		—		6,259		(8)
Total	$	113,891	$	(50)	$	—	$	—	$	113,891	$	(50)

As of December 31, 2019

	Less than 12 Months				12 Months or Greater				Total
			Gross				Gross				Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
	Value		Losses		Value		Losses		Value		Losses
U.S. Treasury securities	$	3,185	$	(2)	$	—	$	—	$	3,185	$	(2)
U.S. government agency obligations		2,400		(1)		—		—		2,400		(1)
Corporate bonds		28,895		(23)		—		—		28,895		(23)
Commercial paper		4,264		(1)		—		—		4,264		(1)
Total	$	38,744	$	(27)	$	—	$	—	$	38,744	$	(27)

As of December 31, 2020 and 2019, respectively, no allowance for credit losses were recognized on the Company’s available-for-sale debt securities as no portion of the unrealized losses associated with those securities were due to credit losses. The information that the Company considered in reaching the conclusion that an allowance for credit losses was not necessary for the following categories of securities is as follows:

As of December 31, 2020 and 2019, the Company held a total of 30 out of 59 positions and 16 out of 81 positions, respectively, that were in an unrealized loss position, none of which had been in an unrealized loss position for

12 months or greater. Unrealized losses individually and in aggregate were not considered to be material for each respective period. Based on the Company’s review of these securities, the Company believes that the cost basis of its available-for-sale marketable securities is recoverable.

U.S. Treasury and U.S. government agency obligations. The unrealized losses on the Company’s investments in direct obligations of the U.S. Treasury and government agencies were due to changes in interest rates and non-credit related factors. The contractual terms of these investments do not permit the issuer to repay principal at a price less than the amortized cost bases of the investments, which is equivalent to the par value on the maturity date. The Company expects to recover the entire amortized cost bases of these securities on the maturity date. The Company does not intend to sell these investments, and it is not more likely than not that the Company will be required to sell these investments before recovery of their amortized cost bases. The Company held 3 out of 6 positions for its U.S Treasury securities, and 1 out of 6 positions for its U.S. government agency obligations, that were in unrealized loss positions as of December 31, 2020.

Corporate bonds, commercial paper, and municipal bonds. The unrealized losses on the Company’s investments in corporate bonds, commercial paper and municipal bonds were due to changes in interest rates and non-credit related factors. The credit ratings of these investments in the Company’s portfolio have not been downgraded below investment grade status. The contractual terms of these investments do not permit the issuer to repay principal at a price less than the amortized cost bases of the investments, which is equivalent to the par value on the maturity date. The Company expects to recover the entire amortized cost bases of these securities on the maturity date. The Company does not intend to sell these investments, and it is not more likely than not that the Company will be required to sell these investments, before recovery of their amortized cost bases. The Company held 8 out of 18 positions for its corporate bonds, 15 out of 22 positions for its commercial paper, and 3 out of 7 positions for its municipal bonds, that were in unrealized loss positions as of December 31, 2020.

The Company classifies its marketable debt securities based on their contractual maturity dates. As of December 31, 2020, the Company’s marketable debt securities mature at various dates through December 2023. The amortized cost and fair values of marketable debt securities by contractual maturity were as follows:

	As of December 31, 2020				As of December 31, 2019
Contractual maturity	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Less than one year	$	149,164	$	149,242	$	136,565	$	136,701
One year to three years		70,570		70,565		63,125		63,159
Total	$	219,734	$	219,807	$	199,690	$	199,860

All available-for-sale marketable securities are classified as Marketable securities, current or Marketable securities, non-current depending on the contractual maturity date of the individual available-for-sale security. Other income, net includes interest and dividends, accretion/amortization of discounts/premiums, realized gains and losses on sales of securities and credit loss expense due to declines in the fair value of securities, if any. The cost of securities sold is based on the specific identification method.

During the year ended December 31, 2020, the Company sold certain shares of its available-for-sale debt securities with a total fair value of $41,600, which resulted in realized gains of $272. There were no sales of available-for-sale marketable securities during the year ended December 31, 2019.

As of December 31, 2020 and 2019, accrued interest receivables on our available-for-sale debt securities were $311 and $971, respectively.