The amortized cost and estimated fair value of investment securities are summarized below. The majority of securities held are

available-for-sale

securities with fair value based on quoted prices for similar assets in active markets or quoted prices for identical assets in markets that are not active. Estimated fair values were obtained from an independent pricing service based upon market quotes.


	March 31, 2021
	Amortized Cost		Gross Unrealized Holding Gain		Gross Unrealized Holding Loss			Fair Value		Total Percent
	(Dollars in thousands)
Investment securities available-for-sale:
Mortgage-backed securities	$	2,175,414	$	38,333	$	(22,409)		$	2,191,338		77.92%
CMO/REMIC		592,915		4,072		(6,821)			590,166		20.99%
Municipal bonds		28,703		1,183		-			29,886		1.06%
Other securities		958		-		-			958		0.03%

Total available-for-sale securities	$	2,797,990	$	43,588	$	(29,230)		$	2,812,348		100.00%

Investment securities held-to-maturity:
Government agency/GSE	$	601,142	$	3,860	$	(16,289	)	$	588,713		55.30%
Mortgage-backed securities		135,137		5,348		(255	)		140,230		12.43%
CMO/REMIC		133,556		2,832		-			136,388		12.29%
Municipal bonds		217,149		5,095		(2,094)			220,150		19.98%

Total held-to-maturity securities	$	1,086,984	$	17,135	$	(18,638)		$	1,085,481		100.00%


	December 31, 2020
	Amortized Cost		Gross Unrealized Holding Gain		Gross Unrealized Holding Loss		Fair Value		Total Percent
	(Dollars in thousands)
Investment securities available-for-sale:
Mortgage-backed securities	$	1,857,030	$	48,006	$	(101)	$	1,904,935		79.41%
CMO/REMIC		457,548		5,515		(249)		462,814		19.29%
Municipal bonds		28,707		1,578		-		30,285		1.26%
Other securities		889		-		-		889		0.04%

Total available-for-sale securities	$	2,344,174	$	55,099	$	(350)	$	2,398,923		100.00%

Investment securities held-to-maturity:
Government agency/GSE	$	98,663	$	5,877	$	-	$	104,540		17.05%
Mortgage-backed securities		146,382		7,644		(32)		153,994		25.30%
CMO/REMIC		145,309		5,202		-		150,511		25.11%
Municipal bonds		188,272		6,980		(74)		195,178		32.54%

Total held-to-maturity securities	$	578,626	$	25,703	$	(106)	$	604,223		100.00%

The following table provides information about the amount of interest income earned on investment securities which is fully taxable and which is exempt from regular federal income tax.


	Three Months Ended
	March 31,
	2021		2020
	(Dollars in thousands)
Investment securities available-for-sale:
Taxable	$	8,968	$	9,825
Tax-advantaged		191		224

Total interest income from available-for-sale securities		9,159		10,049

Investment securities held-to-maturity:
Taxable		2,811		2,698
Tax-advantaged		1,129		1,300

Total interest income from held-to-maturity securities		3,940		3,998

Total interest income from investment securities	$	13,099	$	14,047

The adoption of CECL did not have a material impact on the accounting for investment securities, as approximately 94% of the total investment securities portfolio at March 31, 2021 represents securities issued by the U.S. government or U.S. government-sponsored enterprises, with the implied guarantee of payment of principal and interest. The remaining securities are predominately

AA-

or better general-obligation municipal bonds. The allowance for credit losses for

held-to-maturity

investment securities under the new CECL model was zero at March 31, 2021 and December 31, 2020.

We adopted ASU

2016-13

on January 1, 2020, on a prospective basis. Under this ASU, once it is determined that a credit loss has occurred, an allowance for credit losses is established on our AFS and HTM securities. Management determined that there were no credit losses for securities in an unrealized loss position as of March 31, 2021 and December 31, 2020.

The following table presents the Company’s

available-for-sale

investment securities, by investment category, in an unrealized loss position for which an allowance for credit losses has not been recorded as of March 31, 2021 and December 31, 2020.


	March 31, 2021
	Less Than 12 Months					12 Months or Longer				Total
	Fair Value		Gross Unrealized Holding Losses			Fair Value		Gross Unrealized Holding Losses		Fair Value		Gross Unrealized Holding Losses
	(Dollars in thousands)
Investment securities available-for-sale:
Mortgage-backed securities	$	1,327,126	$	(22,409	)	$	-	$	-	$	1,327,126	$	(22,409	)
CMO/REMIC		422,765		(6,821	)		-		-		422,765		(6,821	)
Municipal bonds		-		-			-		-		-		-

Total available-for-sale securities	$	1,749,891	$	(29,230	)	$	-	$	-	$	1,749,891	$	(29,230	)


	December 31, 2020
	Less Than 12 Months					12 Months or Longer				Total
	Fair Value		Gross Unrealized Holding Losses			Fair Value		Gross Unrealized Holding Losses		Fair Value		Gross Unrealized Holding Losses
	(Dollars in thousands)
Investment securities available-for-sale:
Mortgage-backed securities	$	72,219	$	(101	)	$	-	$	-	$	72,219	$	(101	)
CMO/REMIC		96,974		(249	)		-		-		96,974		(249	)
Municipal bonds		-		-			-		-		-		-

Total available-for-sale securities	$	169,193	$	(350	)	$	-	$	-	$	169,193	$	(350	)

At March 31, 2021 and December 31, 2020, investment securities having a carrying value of approximately $1.92 billion and $1.81 billion, respectively, were pledged to secure public deposits, short and long-term borrowings, and for other purposes as required or permitted by law.

The amortized cost and fair value of debt securities at March 31, 2021, by contractual maturity, are shown in the table below. Although mortgage-backed and CMO/REMIC securities have weighted average remaining contractual maturities of approximately 19 years, expected maturities will differ from contractual maturities because borrowers may have the right to prepay such obligations without penalty. Mortgage-backed and CMO/REMIC securities are included in maturity categories based upon estimated average lives which incorporate estimated prepayment speeds.


	March 31, 2021
	Available-for-sale				Held-to-maturity
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
	(Dollars in thousands)
Due in one year or less	$	4,821	$	4,920	$	4,054	$	4,086
Due after one year through five years		2,368,827		2,383,641		280,057		288,032
Due after five years through ten years		393,699		392,160		133,106		134,081
Due after ten years		30,643		31,627		669,767		659,282

Total investment securities	$	2,797,990	$	2,812,348	$	1,086,984	$	1,085,481

The investment in FHLB stock is periodically evaluated for impairment based on, among other things, the capital adequacy of the FHLB and its overall financial condition. No

impairment losses have been recorded through March 31, 2021.