Short-term Investments

3 Months Ended

Mar. 31, 2021

Short Term Investments [Abstract]

Short-term Investments

5. Short-term Investments

The following is a summary of our short-term investments (in thousands):

	March 31, 2021
			Gross		Gross
	Amortized		Unrealized		Unrealized		Estimated
	Cost		Gains		Losses		Fair Value
U.S. treasury bills and government agency obligations	$	20,061	$	92	$	—	$	20,153
U.S. corporate debt securities		19,064		20		—		19,084
Foreign corporate debt securities		15,501		9		—		15,510
U.S. commercial paper		12,997		—		—		12,997
Foreign commercial paper		38,983		—		—		38,983
Total	$	106,606	$	121	$	—	$	106,727

	December 31, 2020
			Gross		Gross
	Amortized		Unrealized		Unrealized		Estimated
	Cost		Gains		Losses		Fair Value
U.S. treasury bills and government agency obligations	$	20,110	$	166	$	—	$	20,276
U.S. corporate debt securities		11,505		42		—		11,547
Foreign corporate debt securities		15,508		49		—		15,557
U.S. commercial paper		13,997		—		—		13,997
Foreign commercial paper		41,976		—		—		41,976
Total	$	103,096	$	257	$	—	$	103,353

The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. We regularly monitor and evaluate the realizable value of our marketable securities. We did not recognize any impairment losses during the three months ended March 31, 2021 and 2020.

Unrealized gains and losses associated with our investments are reported in accumulated other comprehensive loss. Realized gains and losses associated with our available-for-sale securities, if any, are reported in the statements of operations and comprehensive loss. We did not recognize any realized gains or losses during the three months ended March 31, 2021 and 2020.