Our financial instruments measured at fair value on a recurring basis are cash equivalents and short-term investments.

Our fixed income available-for-sale securities consist of high quality, investment grade securities. We value these securities based on pricing from pricing vendors, who may use quoted prices in active markets for identical assets (Level 1) or inputs other than quoted prices that are observable either directly or indirectly (Level 2) in determining fair value.

Financial instruments are valued based on quoted market prices in active markets include mostly money market securities. Such instruments are generally classified within Level 1 of the fair value hierarchy.

Instruments based on quoted prices in markets that are less active, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency are generally classified within Level 2 of the fair value hierarchy and include U.S. treasury securities.

Instruments valued based on unobservable inputs which reflect the reporting entity’s own assumptions or data that market participants would use in valuing an instrument are generally classified within Level 3 of the fair value hierarchy. As of December 31, 2020, and 2019, we did not hold any Level 3 instruments.

We had no other-than-temporary impairment charges recorded in the years ended December 31, 2020 and 2019.

Financial instruments measured at fair value on a recurring basis as of December 31, 2020 and December 31, 2019 are classified based on the fair value hierarchy in the table below (in thousands):


	December 31, 2020						Total
	Fair Value Measurements Using
	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Money market accounts	$	45,614	$	—	$	—	$	45,614
Total assets at fair value 1	$	45,614	$	—	$	—	$	45,614


	December 31, 2019						Total
	Fair Value Measurements Using
	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Money market accounts	$	63,351	$	—	$	—	$	63,351
U.S. Treasury securities	—		3,019		—		3,019
Total assets at fair value 2	$	63,351	$	3,019	$	—	$	66,370

(2) The above table excludes $23.1 million of cash held in banks as of December 31, 2019.

The contractual maturity dates of our available-for-sale securities on December 31, 2019 and 2020 were all due within one year. There were no transfers of instruments between Level 1 and 2 during the years ended December 31, 2019 and 2020.

Money market accounts are classified as cash equivalents and U.S. Treasury securities (classified as available-for-sale securities), with maturity dates less than one year, are within short-term investments on our Consolidated Balance Sheets.

Short-term investments as of December 31, 2019 consisted of the following (in thousands):


	December 31, 2019
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses		Fair Value
U.S. Treasury securities	$	3,018	$	1	$	—	$	3,019
Total	$	3,018	$	1	$	—	$	3,019