Investments consist of the following as of December 31, 2021 and 2020 (dollars in thousands):

	December 31, 2021
			Gross Unrealized
	Cost		Gain		(Loss)			Fair Value
Short-term investments (available for sale):
Municipal bonds	$	5,028	$	-	$	(1	)	$	5,027
Non-governmental debt securities		168,623		27		(184	)		168,466
Treasury and federal agencies		720		-		-			720
Total short-term investments (available for sale)	$	174,371	$	27	$	(185	)	$	174,213

	December 31, 2020
			Gross Unrealized
	Cost		Gain		(Loss)			Fair Value
Short-term investments (available for sale):
Municipal bonds	$	139	$	1	$	-		$	140
Non-governmental debt securities		288,578		331		(176	)		288,733
Treasury and federal agencies		11,799		6		(2	)		11,803
Total short-term investments (available for sale)	$	300,516	$	338	$	(178	)	$	300,676

In the table above, unrealized holding gains (losses) relate to short-term investments that have been in a continuous unrealized gain (loss) position for less than one year.

Our non-governmental debt securities primarily consist of corporate bonds, certificates of deposit and commercial paper. Our treasury and federal agencies primarily consist of U.S. Treasury bills and federal home loan debt securities. We do not intend to sell our investments in these securities prior to maturity and it is not likely that we will be required to sell these investments before recovery of the amortized cost basis.

A schedule of available-for-sale investments segregated by their original stated terms to maturity as of December 31, 2021 and 2020 are as follows (dollars in thousands):

Less than

one year

One to

five years

Six to

ten years

Greater

than ten

years

Total

Original stated term to maturity of available-for-sale-

investments as of December 31, 2021

133,728

40,485

174,213

Original stated term to maturity of available-for-sale-

investments as of December 31, 2020

182,959

117,641

300,676

Realized gains or losses resulting from sales of investments during the years ended December 31, 2021, 2020 and 2019 were not significant.

FASB ASC Topic 820 – Fair Value Measurements establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets; Level 2, defined as inputs other than quoted prices in active markets that are either directly or indirectly observable; and Level 3, defined as unobservable inputs for which little or no market data exists, therefore requiring an entity to develop its own assumptions.

As of December 31, 2021 and 2020, we held investments that are required to be measured at fair value on a recurring basis. These investments (available for sale) consist of municipal bonds, non-governmental debt securities and treasury and federal agencies securities. Available for sale securities included in Level 2 are estimated based on observable inputs other than quoted prices in active markets for identical assets and liabilities, such as quoted prices for identical or similar assets or liabilities in inactive markets or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

All of our available for sale investments were measured under Level 2 as of December 31, 2021 and December 31, 2020. Additionally, money market funds of $225.3 million and $1.7 million included within cash and cash equivalents on our consolidated balance sheets as of December 31, 2021 and 2020, respectively, were measured under Level 1 and certificates of deposit, commercial paper and treasury bills of $5.1 million included within cash and cash equivalents on our consolidated balance sheets as of December 31, 2020 were measured under Level 2.

Our investment in an equity affiliate, which is recorded within other noncurrent assets on our consolidated balance sheets, represents an international investment in a private company. As of December 31, 2021, our investment in an equity affiliate equated to a 30.7%, or $3.2 million, non-controlling interest in CCKF, a Dublin-based educational technology company providing intelligent systems to power the delivery of individualized and personalized learning.

We recorded a gain of approximately $0.2 million each for the years ended December 31, 2021 and 2020, respectively, and recorded a gain of approximately $0.1 million for the year ended December 31, 2019, related to our proportionate investment in CCKF within miscellaneous income on our consolidated statements of income.

We make periodic operating maintenance payments to CCKF related to proprietary rights that we use in our intellipath^® personalized learning technology. The total fees recorded for the years ended December 31, 2021, 2020 and 2019 were as follows (dollars in thousands):