The amortized cost, gross unrealized gains and losses and estimated fair values of debt securities available for sale and equity securities with a readily determinable fair value as of December 31, 2019, and December 31, 2018, are summarized in the table below, in thousands:


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
December 31, 2019
U.S. government corporations and agencies	$	9,844	$	49	$	—	$	9,893
Mortgage and asset-backed securities	2,579,081		17,200		(19,003)		2,577,278
Obligations of states and political subdivisions	704,073		12,516		(9,399)		707,190

Total debt securities	3,292,998		29,765		(28,402)		3,294,361
Equity securities with a readily determinable fair value	18,435		—		—		18,435
Total	$	3,311,433	$	29,765	$	(28,402)	$	3,312,796
December 31, 2018
U.S. government corporations and agencies	$	32,075	$	3	$	(127)	$	31,951
Mortgage and asset-backed securities	2,061,358		3,740		(38,400)		2,026,698
Obligations of states and political subdivisions	382,101		919		(8,046)		374,974

Total debt securities	2,475,534		4,662		(46,573)		2,433,623
Equity securities	17,086		—		—		17,086
Total	$	2,492,620	$	4,662	$	(46,573)	$	2,450,709

On January 1, 2019, Heartland adopted ASU 2017-12, and as a result of the adoption, $148.0 million of held to maturity debt securities were transferred to debt securities available for sale. The securities were transferred at book value on the date of the transfer.

Equity securities include money market accounts that totaled $18.4 million at carrying value and $18.4 million at fair value at December 31, 2019. The portion of unrealized net gains on equity securities recognized in current earnings during 2019, which related to securities still held at December 31, 2019, totaled $525,000.


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
December 31, 2019

Obligations of states and political subdivisions	$	91,324	$	9,160	$	—	$	100,484
Total	$	91,324	$	9,160	$	—	$	100,484
December 31, 2018

Obligations of states and political subdivisions	$	236,283	$	9,554	$	(496)	$	245,341
Total	$	236,283	$	9,554	$	(496)	$	245,341

The amortized cost and estimated fair value of investment securities carried at fair value at December 31, 2019, by contractual maturity are as follows, in thousands. Expected maturities will differ from contractual maturities because issuers may have the right to call or prepay obligations with or without penalties.


	December 31, 2019
	Amortized Cost		Estimated Fair Value
Due in 1 year or less	$	12,121	$	12,171
Due in 1 to 5 years	28,111		28,434
Due in 5 to 10 years	76,299		77,942
Due after 10 years	597,386		598,536
Total debt securities	713,917		717,083
Mortgage and asset-backed securities	2,579,081		2,577,278
Equity securities with a readily determinable fair value	18,435		18,435
Total investment securities	$	3,311,433	$	3,312,796

The amortized cost and estimated fair value of debt securities held to maturity at December 31, 2019, by contractual maturity are as follows, in thousands. Expected maturities will differ from contractual maturities because issuers may have the right to call or prepay obligations with or without penalties.


	December 31, 2019
	Amortized Cost		Estimated Fair Value
Due in 1 year or less	$	2,443	$	2,472
Due in 1 to 5 years	17,604		18,153
Due in 5 to 10 years	59,708		64,775
Due after 10 years	11,569		15,084


Total investment securities	$	91,324	$	100,484

The following tables summarize, in thousands, the amount of unrealized losses, defined as the amount by which cost or amortized cost exceeds fair value, and the related fair value of investments with unrealized losses in Heartland's securities portfolio as of December 31, 2019, and December 31, 2018. The investments were segregated into two categories: those that have been in a continuous unrealized loss position for less than 12 months and those that have been in a continuous unrealized loss position for 12 or more months. The reference point for determining how long an investment was in an unrealized loss position was December 31, 2019, and December 31, 2018, respectively. Securities for which Heartland has taken credit-related other-than-temporary impairment ("OTTI") write-downs are categorized as being "less than 12 months" or "12 months or longer" in a continuous loss position based on the point in time that the fair value declined to below the cost basis and not the period of time since the credit-related OTTI write-down.


Debt securities available for sale	Less than 12 months						12 months or longer						Total
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
December 31, 2019
U.S. government corporations and agencies	$	—	$	—	$	—	$	—	$	—	$	—
Mortgage and asset-backed securities	1,231,732		(14,189)		241,232		(4,814)		1,472,964		(19,003)
Obligations of states and political subdivisions	387,534		(9,399)		—		—		387,534		(9,399)



Total temporarily impaired securities	$	1,619,266	$	(23,588)	$	241,232	$	(4,814)	$	1,860,498	$	(28,402)
December 31, 2018
U.S. government corporations and agencies	$	24,902	$	(83)	$	4,577	$	(44)	$	29,479	$	(127)
Mortgage and asset-backed securities	733,826		(9,060)		805,089		(29,340)		1,538,915		(38,400)
Obligations of states and political subdivisions	34,990		(390)		258,143		(7,656)		293,133		(8,046)



Total temporarily impaired securities	$	793,718	$	(9,533)	$	1,067,809	$	(37,040)	$	1,861,527	$	(46,573)


Securities held to maturity	Less than 12 months						12 months or longer						Total
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
December 31, 2019

Obligations of states and political subdivisions	$	—	$	—	$	—	$	—	$	—	$	—
Total temporarily impaired securities	$	—	$	—	$	—	$	—	$	—	$	—
December 31, 2018

Obligations of states and political subdivisions	$	10,802	$	(17)	$	19,508	$	(479)	$	30,310	$	(496)
Total temporarily impaired securities	$	10,802	$	(17)	$	19,508	$	(479)	$	30,310	$	(496)

Heartland reviews the investment securities portfolio on a quarterly basis to monitor its exposure to OTTI. A determination as to whether a security's decline in fair value is other-than-temporary takes into consideration numerous factors and the relative significance of any single factor can vary by security. Some factors Heartland may consider in the OTTI analysis include the length of time the security has been in an unrealized loss position, changes in security ratings, financial condition of the issuer, as well as security and industry specific economic conditions. In addition, with regard to debt securities, Heartland may also evaluate payment structure, whether there are defaulted payments or expected defaults, prepayment speeds and the value of any underlying collateral. For certain debt securities in unrealized loss positions, Heartland prepares cash flow analyses to compare the present value of cash flows expected to be collected from the security with the amortized cost basis of the security.

Included in other securities were shares of stock in each Federal Home Loan Bank (the "FHLB") of Des Moines, Chicago, Dallas, San Francisco and Topeka at an amortized cost of $16.8 million at December 31, 2019 and $16.6 million at December 31, 2018.

The Heartland banks are required to maintain FHLB stock as members of the various FHLBs as required by these institutions. These equity securities are "restricted" in that they can only be sold back to the respective institutions or another member institution at par. Therefore, they are less liquid than other marketable equity securities and their fair value approximates amortized cost. Heartland considers its FHLB stock as a long-term investment that provides access to competitive products and liquidity. Heartland evaluates impairment in these investments based on the ultimate recoverability of the par value and at December 31, 2019, did not consider the investments to be other than temporarily impaired.