
December 31, 2019	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Corporate bonds	$	210,891	$	142	$	(27)	$	211,006
U.S. government treasury bonds	70,587		65		(2)		70,650
U.S. government agency bonds	22,085		17		(1)		22,101
Commercial paper	14,426		—		—		14,426
Certificates of deposit	19		—		—		19
Total marketable securities, short-term	$	318,008	$	224	$	(30)	$	318,202

Cash equivalents are not included in the table above as the gross unrealized gains and losses are not material. We had no short-term marketable securities that have been in a continuous material unrealized loss position for greater than twelve months as of December 31, 2019. Amounts reclassified to earnings from accumulated other comprehensive income (loss), net related to unrealized gains or losses were not material for the three and nine months ended September 30, 2020 and 2019. For the three and nine months ended September 30, 2020 and 2019, realized gains or losses were not material.

Our fixed-income securities investment portfolio allows for investments with a maximum effective maturity of up to 40 months on any individual security. The securities that we invest in are generally deemed to be low risk based on their credit ratings from the major rating agencies. The longer the duration of these securities, the more susceptible they are to changes in market interest rates and bond yields. As interest rates increase, those securities purchased at a lower yield show a mark-to-market unrealized loss which are primarily due to changes in interest rates and credit spreads. We expect to realize the full value of all these investments upon maturity or sale. The weighted average remaining duration of these securities was approximately seven months as of December 31, 2019.

As the carrying value approximates the fair value for our short-term marketable securities shown in the table above, the fair value of our short-term marketable securities as of December 31, 2019 had a contractual maturity one year or less.

The following tables summarize our financial assets measured at fair value on a recurring basis as of September 30, 2020 and December 31, 2019 (in thousands):


Description	Balance as of September 30, 2020		Level 1		Level 2		Level 3
Cash equivalents:
Money market funds	$	285,228	$	285,228	$	—	$	—























Prepaid expenses and other current assets:
Israeli funds	3,399		—		3,399		—


Current unsecured promissory note	14,505		—		—		14,505


	$	303,132	$	285,228	$	3,399	$	14,505


Description	Balance as of December 31, 2019		Level 1		Level 2		Level 3
Cash equivalents:
Money market funds	$	236,923	$	236,923	$	—	$	—



Short-term investments:
Corporate bonds	211,006		—		211,006		—
Commercial paper	14,426		—		14,426		—
U.S. government treasury bonds	70,650		70,650		—		—


U.S. government agency bonds	22,101		—		22,101		—
Certificates of deposit	19		—		19		—








Prepaid expenses and other current assets:
Israeli funds	3,226		—		3,226		—

Current unsecured promissory note	25,005		—		—		25,005
Other assets:
Long-term unsecured promissory note	7,328		—		—		7,328
	$	590,684	$	307,573	$	250,778	$	32,333

The unsecured promissory note that was entered into in 2019 with SmileDirectClub, LLC (“SDC”) is classified as Level 3 in our fair value hierarchy as financial information of third parties may not be timely available and consequently we estimate the fair value based on the best available information at the measurement date. The original amount of the note was $54.2 million which has decreased due to payments received. Refer to Note 6 “Equity Method Investments” of the Notes to Condensed Consolidated Financial Statements for more information.

Our investments in equity securities of privately held companies without readily determinable fair values were $2.1 million and $5.9 million as of September 30, 2020 and December 31, 2019, respectively, and are reported as nonrecurring investments within other assets in our Condensed Consolidated Balance Sheet. Our investments in equity securities are considered Level 3 in the fair value hierarchy since the investments are in private companies without quoted market prices and we adjust the carrying value based on observable price changes. During the nine months ended September 30, 2020 and September 30, 2019, we recorded impairment losses of $3.8 million and $4.0 million, respectively, resulting from observable price changes.

We enter into foreign currency forward contracts to minimize the short-term impact of foreign currency exchange rate fluctuations on certain trade and intercompany receivables and payables. These forward contracts are classified within Level 2 of the fair value hierarchy. As a result of the settlement of foreign currency forward contracts, during the three months ended September 30, 2020 and 2019, we recognized net losses of $12.1 million and net gains of $10.1 million, respectively, and during the nine months ended September 30, 2020 and 2019, we recognized net gains of $0.6 million and $10.5 million,

The following table presents the gross notional value of all our foreign exchange forward contracts outstanding as of September 30, 2020 and December 31, 2019 (in thousands):


	September 30, 2020
	Local Currency Amount	Notional Contract Amount (USD)
Chinese Yuan	¥1,075,000	$	158,198
Euro	€127,000	148,852
Canadian Dollar	C$77,000	57,570
British Pound	£29,200	37,524
Japanese Yen	¥3,385,000	32,042
Brazilian Real	R$112,500	19,899
Israeli Shekel	ILS53,000	15,441
Mexican Peso	M$140,000	6,266
Australian Dollar	A$6,900	4,925
Swiss Franc	CHF4,000	4,343
		$	485,060


	December 31, 2019
	Local Currency Amount	Notional Contract Amount (USD)
Euro	€97,000	$	108,870
Chinese Yuan	¥431,000	60,702
Canadian Dollar	C$52,000	39,802
British Pound	£28,000	36,770
Brazilian Real	R$130,000	32,185
Japanese Yen	¥3,000,000	27,604
Israeli Shekel	ILS63,700	18,439
Mexican Peso	M$140,000	7,398
Australian Dollar	A$3,000	2,101
		$	333,871

Prior to the closing of the exocad acquisition on April 1, 2020, we entered into a Euro foreign currency forward contract with a notional contract amount of €376.0 million. During the nine months ended September 30, 2020, we recognized a $10.2 million loss within other income (expense), net in our Condensed Consolidated Statement of Operations.