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 that are carried at fair value as of September 30, 2019, and December 31, 2018, are summarized in the table below, in thousands:


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
September 30, 2019
U.S. government corporations and agencies	$	8,900	$	50	$	—	$	8,950
Mortgage and asset-backed securities	2,465,561		28,381		(13,265)		2,480,677
Obligations of states and political subdivisions	500,222		13,915		(1,558)		512,579

Total debt securities	2,974,683		42,346		(14,823)		3,002,206
Equity securities with a readily determinable fair value	18,362		—		—		18,362
Total	$	2,993,045	$	42,346	$	(14,823)	$	3,020,568
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 with a readily determinable fair value	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.


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
September 30, 2019

Obligations of states and political subdivisions	$	87,965	$	9,940	$	—	$	97,905
Total	$	87,965	$	9,940	$	—	$	97,905
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 September 30, 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.


	September 30, 2019
	Amortized Cost		Estimated Fair Value
Due in 1 year or less	$	22,717	$	22,750
Due in 1 to 5 years	23,369		23,725
Due in 5 to 10 years	76,723		79,411
Due after 10 years	386,313		395,643
Total debt securities	509,122		521,529
Mortgage and asset-backed securities	2,465,561		2,480,677
Equity securities with a readily determinable fair value	18,362		18,362
Total investment securities	$	2,993,045	$	3,020,568

The amortized cost and estimated fair value of debt securities held to maturity at September 30, 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.


	September 30, 2019
	Amortized Cost		Estimated Fair Value
Due in 1 year or less	$	2,403	$	2,443
Due in 1 to 5 years	15,153		15,690
Due in 5 to 10 years	58,936		64,695
Due after 10 years	11,473		15,077


Total investment securities	$	87,965	$	97,905

As of September 30, 2019, and December 31, 2018, securities with a fair value of $431.5 million and $524.8 million, respectively, were pledged to secure public and trust deposits, short-term borrowings and for other purposes as required or permitted by law.


	Three Months Ended September 30,						Nine Months Ended September 30,
	2019		2018		2019		2018
Proceeds from sales	$	290,877	$	59,137	$	1,485,773	$	694,872
Gross security gains	2,371		67		10,301		3,537
Gross security losses	358		212		3,133		2,500

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 September 30, 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 months or more. The reference point for determining how long an investment was in an unrealized loss position was September 30, 2018, and December 31, 2017, 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
September 30, 2019
U.S. government corporations and agencies	$	—	$	—	$	—	$	—	$	—	$	—
Mortgage and asset-backed securities	976,443		(7,689)		255,827		(5,576)		1,232,270		(13,265)
Obligations of states and political subdivisions	118,741		(1,525)		2,139		(33)		120,880		(1,558)



Total temporarily impaired securities	$	1,095,184	$	(9,214)	$	257,966	$	(5,609)	$	1,353,150	$	(14,823)
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
September 30, 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.

The remaining unrealized losses on Heartland's mortgage and asset-backed securities are the result of changes in market interest rates or widening of market spreads subsequent to the initial purchase of the securities. The losses are not related to concerns regarding the underlying credit of the issuers or the underlying collateral. It is expected that the securities will not be settled at a price less than the amortized cost of the investment. Because the decline in fair value is attributable to changes in interest rates or widening market spreads and not credit quality, and because Heartland has the intent and ability to hold these investments until a market price recovery or to maturity and does not believe it will be required to sell the securities before maturity, these investments are not considered other-than-temporarily impaired.

The remaining unrealized losses on Heartland's obligations of states and political subdivisions are the result of changes in market interest rates or widening of market spreads subsequent to the initial purchase of the securities. Management monitors the published credit ratings of these securities and the stability of the underlying municipalities. Because the decline in fair value is attributable to changes in interest rates or widening market spreads due to insurance company downgrades and not underlying credit quality, and because Heartland has the intent and ability to hold these investments until a market price recovery or to maturity and does not believe it will be required to sell the securities before maturity, these investments are not considered other-than-temporarily impaired.

There were no gross realized gains or losses on the sale of securities carried at fair value or held to maturity securities with OTTI write-downs for the nine-month periods ended September 30, 2019, and September 30, 2018, respectively.

Other investments, at cost, include equity securities without a readily determinable fair value, which totaled $29.0 million and $28.4 million at September 30, 2019, and December 31, 2018, respectively. At September 30, 2019, and December 31, 2018, other investments at cost included shares of stock in the Federal Home Loan Banks (the "FHLBs") of Des Moines, Chicago, Dallas, San Francisco and Topeka at an amortized cost of $14.9 million and $16.6 million, respectively.

The Heartland banks are required by federal law to maintain FHLB stock as members of the various FHLBs. These equity securities are "restricted" in that they can only be sold back to the respective institutions from which they were acquired or another member institution at par. Therefore, the FHLB stock is less liquid than other marketable equity securities, and the 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 September 30, 2019, did not consider the investments to be other than temporarily impaired.