ASC 820 defines fair value, establishes a consistent framework for measuring fair value and requires disclosure about fair value measurements. ASC 820, among other things, requires us to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. In addition, ASC 820 precludes the use of block discounts when measuring the fair value of instruments traded in an active market, which were previously applied to large holdings of publicly traded equity securities.

We determine the fair value of our financial instruments based on the fair value hierarchy established in ASC 820. In accordance with ASC 820, we utilize the following fair value hierarchy:

This hierarchy requires the use of observable market data when available.

Under ASC 820, we determine fair value based on the price that would be received for an asset or paid to transfer a liability in an orderly transaction between market participants on the measurement date. It is our policy to maximize the use of observable inputs and minimize the use of unobservable inputs when developing fair value measurements, in accordance with the fair value hierarchy described above. Fair value measurements for assets and liabilities where there exists limited or no observable market data are calculated based upon our pricing policy, the economic and competitive environment, the characteristics of the asset or liability and other factors as appropriate. These estimated fair values may not be realized upon actual sale or immediate settlement of the asset or liability.

Where quoted prices are available on active exchanges for identical instruments, investment securities are classified within Level 1 of the valuation hierarchy. Level 1 investment securities include equity securities.

Level 2 investment securities include corporate bonds, collateralized corporate bank loans, municipal bonds, U.S. Treasury securities, other obligations of the U.S. Government and mortgage-backed securities for which quoted prices are not available on active exchanges for identical instruments. We use third-party pricing services to determine fair values for each Level 2 investment security in all asset classes. Since quoted prices in active markets for identical assets are not available, these prices are determined using observable market information such as quotes from less active markets and/or quoted prices of securities with similar characteristics, among other things. We have reviewed the processes used by the pricing services and have determined that they result in fair values consistent with the requirements of ASC 820 for Level 2 investment securities. We have not adjusted any prices received from third-party pricing sources. There were no transfers between Level 1 and Level 2 securities.

In cases where there is limited activity or less transparency around inputs to the valuation, investment securities are classified within Level 3 of the valuation hierarchy. Level 3 investments are valued based on the best available data in order to approximate fair value. This data may be internally developed and consider risk premiums that a market participant would require. Investment securities classified within Level 3 include other less liquid investment securities.

The following table presents, for each of the fair value hierarchy levels, assets that are measured at fair value on a recurring basis at September 30, 2021 and December 31, 2020 (in thousands):


	As of September 30, 2021
	Quoted Prices in
	Active Markets for
	Identical Assets		Other Observable		Unobservable
	(Level 1)		Inputs (Level 2)		Inputs (Level 3)		Total
U.S. Treasury securities and obligations of U.S. Government	$	—	$	66,496	$	—	$	66,496
Corporate bonds		—		121,741		356		122,097
Corporate bank loans		—		86,334		—		86,334
Municipal bonds		—		40,971		—		40,971
Mortgage-backed		—		2,018		—		2,018
Total debt securities		—		317,560		356		317,916
Total equity securities		45,362		—		—		45,362
Total investments	$	45,362	$	317,560	$	356	$	363,278


	As of December 31, 2020
	Quoted Prices in
	Active Markets for
	Identical Assets		Other Observable		Unobservable
	(Level 1)		Inputs (Level 2)		Inputs (Level 3)		Total
U.S. Treasury securities and obligations of U.S. Government	$	—	$	179,746	$	—	$	179,746
Corporate bonds		—		219,020		348		219,368
Corporate bank loans		—		52,782		—		52,782
Municipal bonds		—		50,539		—		50,539
Mortgage-backed		—		4,844		—		4,844
Total debt securities		—		506,931		348		507,279
Total equity securities		29,388		—		—		29,388
Total investments	$	29,388	$	506,931	$	348	$	536,667

Due to significant unobservable inputs into the valuation model for one corporate bond as of September 30, 2021 and December 31, 2020, we classified this investment as Level 3 in the fair value hierarchy. The corporate bond is a convertible senior note and its fair value was estimated by the sum of the bond value using an income approach discounting the scheduled interest and principal payments and the conversion feature utilizing a binomial lattice model.

The following table summarizes the changes in fair value for all financial assets measured at fair value on a recurring basis using significant unobservable inputs (Level 3) during the nine months ended September 30, 2021 and 2020 (in thousands):


Beginning balance as of January 1, 2021	$	348
Sales		—
Settlements		—
Purchases		—
Issuances		—
Total realized/unrealized losses included in net income		—
Net gain included in other comprehensive income		8
Transfers into Level 3		—
Transfers out of Level 3		—
Ending balance as of September 30, 2021	$	356


Beginning balance as of January 1, 2020	$	339
Sales		—
Settlements		—
Purchases		—
Issuances		—
Total realized/unrealized gains included in net loss		—
Net gains included in other comprehensive loss		(14)
Transfers into Level 3		—
Transfers out of Level 3		—
Ending balance as of September 30, 2020	$	325