Short-Term Investments

12 Months Ended

Dec. 31, 2021

Investments, Debt and Equity Securities [Abstract]

The Company invests in marketable securities primarily consisting of debt instruments of the U.S. Government, U.S. Government-sponsored enterprises, and financial institutions and corporations with strong credit ratings. The following represents a summary of the estimated fair value of short-term investments at December 31, 2021 and 2020 (in thousands):


At December 31, 2021	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Estimated Fair Value
Available-for-sale securities:
U.S. Treasury securities	$	222,206	$	—	$	(482)	$	221,724
Commercial paper	218,391		14		(24)		218,381
Corporate debt securities	58,881		—		(45)		58,836
U.S. Government-sponsored enterprises	50,773		1		(88)		50,686
Supranational bonds	3,003		—		—		3,003
Total	$	553,254	$	15	$	(639)	$	552,630


At December 31, 2020	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Estimated Fair Value
Available-for-sale securities:
U.S. Treasury securities	$	143,244	$	12	$	(2)	$	143,254
Commercial paper	108,892		5		(1)		108,896
Corporate debt securities	85,788		48		(13)		85,823
U.S. Government-sponsored enterprises	52,330		21		(1)		52,350
Total	$	390,254	$	86	$	(17)	$	390,323

The contractual maturities of available-for-sale debt securities as of December 31, 2021, were as follows (in thousands):


	Years to Maturity
At December 31, 2021	Within One Year		One to Two Years		Estimated Fair Value
U.S. Treasury securities	$	105,231	$	116,493	$	221,724
Commercial paper	218,381		—		218,381
Corporate debt securities	58,836		—		58,836
U.S. Government-sponsored enterprises	32,282		18,404		50,686
Supranational bonds	3,003		—		3,003
Total	$	417,733	$	134,897	$	552,630

The Company has classified all marketable securities, regardless of maturity, as short-term investments based upon the Company’s ability and intent to use any of those marketable securities to satisfy the Company’s liquidity requirements.

The Company reviews the portfolio of available-for-sale debt securities quarterly to determine if any investment is impaired due to changes in credit risk or other potential valuation concerns. Unrealized losses on available-for-sale debt securities at December 31, 2021 were not significant and were primarily due to changes in market interest rates. The Company does not intend to sell the available-for-sale debt securities that are in an unrealized loss position, and it is not more likely than not that the Company will be required to sell these debt securities before recovery of their amortized cost bases, which may be at maturity. Based on the credit quality of the available-for-sale debt securities in an unrealized loss position, and the Company’s estimates of future cash flows to be collected from those securities, the Company believes the unrealized losses are not credit losses. Accordingly, the Company did not recognize any impairment losses related to its available-for-sale debt securities at December 31, 2021.