(2) Investment Securities

The amortized cost and estimated fair value by type of investment security at December 31, 2018 are as follows:


	Held to Maturity
			Gross		Gross
	Amortized		unrealized		unrealized		Estimated		Carrying
	cost		gains		losses		fair value		value
	(Dollars in Thousands)
Other securities	$	1,200	$	—	$	—	$	1,200	$	1,200
Total investment securities	$	1,200	$	—	$	—	$	1,200	$	1,200


	Available for Sale Debt Securities
			Gross		Gross
	Amortized		unrealized		unrealized		Estimated		Carrying
	cost		gains		losses		fair value		value(1)
	(Dollars in Thousands)
Residential mortgage-backed securities	$	3,295,366	$	6,813	$	(79,169)	$	3,223,010	$	3,223,010
Obligations of states and political subdivisions		185,799		2,646		(105)		188,340		188,340
Total investment securities	$	3,481,165	$	9,459	$	(79,274)	$	3,411,350	$	3,411,350

(1)

Included in the carrying value of residential mortgage‑ backed securities are $501,293 of mortgage‑backed securities issued by Ginnie Mae and $2,721,717 of mortgage‑backed securities issued by Fannie Mae and Freddie Mac

The amortized cost and estimated fair value of investment securities at December 31, 2018, by contractual maturity, are shown below. Expected maturities will differ from contractual maturities because borrowers may have the right to prepay obligations with or without prepayment penalties.


	Held to Maturity				Available for Sale
	Amortized		Estimated		Amortized		Estimated
	Cost		fair value		Cost		fair value
	(Dollars in Thousands)
Due in one year or less	$	—	$	—	$	—	$	—
Due after one year through five years		1,200		1,200		—		—
Due after five years through ten years		—		—		500		502
Due after ten years		—		—		185,299		187,838
Residential mortgage-backed securities		—		—		3,295,366		3,223,010
Total investment securities	$	1,200	$	1,200	$	3,481,165	$	3,411,350

The amortized cost and estimated fair value by type of investment security at December 31, 2017 are as follows:


	Held to Maturity
			Gross		Gross
	Amortized		unrealized		unrealized		Estimated		Carrying
	cost		gains		losses		fair value		value
	(Dollars in Thousands)
Other securities	$	2,400	$	—	$	—	$	2,400	$	2,400
Total investment securities	$	2,400	$	—	$	—	$	2,400	$	2,400


	Available for Sale
			Gross		Gross		Estimated
	Amortized		unrealized		unrealized		fair		Carrying
	cost		gains		losses		value		value(1)
	(Dollars in Thousands)
Residential mortgage-backed securities	$	3,943,092	$	14,110	$	(65,969)	$	3,891,233	$	3,891,233
Obligations of states and political subdivisions		225,096		7,871		(16)		232,951		232,951
Equity securities		28,075		293		(482)		27,886		27,886
Total investment securities	$	4,196,263	$	22,274	$	(66,467)	$	4,152,070	$	4,152,070

(1)

Included in the carrying value of residential mortgage‑ backed securities are $654,063 of mortgage‑backed securities issued by Ginnie Mae, $3,237,1700 of mortgage‑backed securities issued by Fannie Mae and Freddie Mac

Residential mortgage‑backed securities are securities issued by Freddie Mac, Fannie Mae, Ginnie Mae or non‑government entities. Investments in residential mortgage‑backed securities issued by Ginnie Mae are fully guaranteed by the U.S. government. Investments in mortgage‑backed securities issued by Freddie Mac and Fannie Mae are not fully guaranteed by the U.S. government; however, we believe that the quality of the bonds is similar to other AAA rated bonds with limited credit risk, particularly given the placement of Fannie Mae and Freddie Mac into conservatorship by the federal government in early September 2008 and because securities issued by others that are collateralized by residential mortgage‑backed securities issued by Fannie Mae and Freddie Mac are rated consistently as AAA rated securities.

The amortized cost and fair value of available for sale investment securities pledged to qualify for fiduciary powers, to secure public monies as required by law, repurchase agreements and short‑term fixed borrowings was $1,112,852,000 and $1,086,360,000, respectively, at December 31, 2018.

Proceeds from the sale and call of securities available‑for‑sale were $59,782,000, $396,066,000 and $352,743,000 during 2018, 2017 and 2016, respectively, which amounts included $0, $377,756,000 and $338,138,000 of mortgage‑backed securities. Gross gains of $3,000, $1,186,000 and $586,000, and gross losses of $144,000, $5,960,000 and $3,212,000 were realized on the sales in 2018, 2017 and 2016, respectively.

Gross unrealized losses on investment securities and the fair value of the related securities, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at December 31, 2018 were as follows:


	Less than 12 months				12 months or more				Total
			Unrealized				Unrealized				Unrealized
	Fair Value		Losses		Fair Value		Losses		Fair Value		Losses
	(Dollars in Thousands)
Available for sale:
Residential mortgage-backed securities	$	208,384	$	(2,124)	$	2,537,181	$	(77,045)	$	2,745,565	$	(79,169)
Obligations of states and political subdivisions		12,756		(99)		512		(6)		13,268		(105)
	$	221,140	$	(2,223)	$	2,537,693	$	(77,051)	$	2,758,833	$	(79,274)

Gross unrealized losses on investment securities and the fair value of the related securities, aggregated by investment category and length of time that individual securities have been in a continuous loss position, at December 31, 2017 were as follows:


	Less than 12 months				12 months or more				Total
			Unrealized				Unrealized				Unrealized
	Fair Value		Losses		Fair Value		Losses		Fair Value		Losses
	(Dollars in Thousands)
Available for sale:
Residential mortgage-backed securities	$	1,061,577	$	(13,157)	$	2,029,455	$	(52,812)	$	3,091,032	$	(65,969)
Obligations of states and political subdivisions		5,534		(9)		522		(7)		6,056		(16)
Equity securities		11,499		(251)		8,019		(231)		19,518		(482)
	$	1,078,610	$	(13,417)	$	2,037,996	$	(53,050)	$	3,116,606	$	(66,467)

The unrealized losses on investments in residential mortgage‑backed securities are primarily caused by changes in market interest rates. Residential mortgage‑backed securities are primarily securities issued by Freddie Mac, Fannie Mae and Ginnie Mae. The contractual cash obligations of the securities issued by Ginnie Mae are fully guaranteed by the U.S. government. The contractual cash obligations of the securities issued by Freddie Mac and Fannie Mae are not fully guaranteed by the U.S. government; however, we believe that the quality of the bonds is similar to other AAA rated bonds with limited credit risk, particularly given the placement of Fannie Mae and Freddie Mac into conservatorship by the federal government in early September 2008 and because securities issued by others that are collateralized by residential mortgage‑backed securities issued by Fannie Mae and Freddie Mac are rated consistently as AAA rated securities. The decrease in fair value on residential mortgage‑backed securities issued by Freddie Mac, Fannie Mae and Ginnie Mae is due to market interest rates. We have no intent to sell and more likely than not be required to sell before a market price recovery or maturity of the securities; therefore, it is our conclusion that the investments in residential mortgage‑backed securities issued by Freddie Mac, Fannie Mae and Ginnie Mae are not considered other‑than‑temporarily impaired. In addition, we had a small investment in non‑agency residential mortgage‑backed securities that had additional market volatility beyond economically induced interest rate events, which were sold in the first quarter of 2017. We concluded that the investments in non‑agency residential mortgage‑backed securities were other‑than‑temporarily impaired due to both credit and other than credit issues. No impairment charges were recorded in 2017. Impairment charges of $354,000 ($230,100, after tax) were recorded in 2016 on the non‑agency residential mortgage backed securities. The impairment charges represent the credit related impairment on the securities.

The unrealized losses on investments in other securities are caused by fluctuations in market interest rates. The underlying cash obligations of the securities are guaranteed by the entity underwriting the debt instrument. We believe that the entity issuing the debt will honor its interest payment schedule, as well as the full debt at maturity. We purchased the securities for their economic value. The decrease in fair value is primarily due to market interest rates and not other factors, and because we have no intent to sell and will more likely than not be required to sell before a market price recovery or maturity of the securities, it is our conclusion that the investments are not considered other‑than‑temporarily impaired.

The following table presents a reconciliation of credit‑related impairment charges on available‑for‑sale investments recognized in earnings for the twelve months ended December 31, 2017 (in Thousands):


Balance at December 31, 2016	$	13,931
Sale of other-than-temporarily impaired available-for-sale securities during period		(13,931)
Balance at December 31, 2017	$	—


Balance at December 31, 2015	$	13,577
Impairment charges recognized during period		354
Balance at December 31, 2016	$	13,931

Equity securities with readily determinable fair values consist primarily of Community Reinvestment Act funds. At December 31, 2018 and December 31, 2017, the balance in equity securities with readily determinable fair values recorded at fair value were $5,937,000 and $27,886,000, respectively. Prior to January 1, 2018, the equity securities were included in available-for-sale securities, with the related unrealized gain or loss recorded as a component of other comprehensive income (loss). The following is a summary of unrealized and realized gains and losses recognized in net income on equity securities during the twelve months ended December 31, 2018:


	Year Ended
	December 31,
	(Dollars in Thousands)
	2018
Net losses recognized during the period on equity securities	$	(388)
Less: Net gains and (losses) recognized during the period on equity securities sold during the period		—

Unrealized losses recognized during the reporting period on equity securities still held at the reporting date	$	(388)