Financial Instruments

3 Months Ended

Mar. 31, 2021

Investments All Other Investments [Abstract]

Financial Instruments

4. Financial Instruments

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

March 31, 2021	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Money market funds (cash equivalents)	$	83,044	$	—	$	—	$	83,044
U.S. government agency securities		16,804		3		—		16,807
Federal agency securities		7,147		2		—		7,149
Total financial assets	$	106,995	$	5	$	—	$	107,000
Classified as:
Cash and cash equivalents							$	83,044
Short-term investments								23,956
							$	107,000

December 31, 2020	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Money market funds (cash equivalents)	$	30,360	$	—	$	—	$	30,360
U.S. government agency securities		37,835		2		—		37,837
Federal agency securities		13,697		3		—		13,700
Total financial assets	$	81,892	$	5	$	—	$	81,897
Classified as:
Cash and cash equivalents							$	30,360
Short-term investments								48,994
Long-term investments								2,543
							$	81,897

There have been no material realized gains or losses on available-for-sale debt securities for the periods presented. As of March 31, 2021, the remaining contractual maturities of $24.0 million of available-for-sale debt securities was less than one year.

The carrying amounts of cash and cash equivalents, accounts receivable, accounts payable, and accrued liabilities approximate their fair values due to the short-term maturity of these instruments.