Investment Securities (Tables)

6 Months Ended

Jun. 30, 2022

Investments, Debt and Equity Securities [Abstract]

Summary of Amortized Cost and Estimated Fair Value of Investment Securities

Estimated fair values were obtained from an independent pricing service based upon market quotes.

	June 30, 2022
	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	$	3,386,552	$	423	$	(278,060	)	$	3,108,915		85.74	%
CMO/REMIC		557,723		8		(67,601	)		490,130		13.52	%
Municipal bonds		27,139		100		(1,150	)		26,089		0.72	%
Other securities		1,023		-		-			1,023		0.02	%
Total available-for-sale securities	$	3,972,437	$	531	$	(346,811	)	$	3,626,157		100.00	%
Investment securities held-to-maturity:
Government agency/GSE	$	562,287	$	359	$	(82,668	)	$	479,978		23.31	%
Mortgage-backed securities		688,320		159		(74,344	)		614,135		28.53	%
CMO/REMIC		799,591		-		(83,786	)		715,805		33.15	%
Municipal bonds		362,110		245		(38,090	)		324,265		15.01	%
Total held-to-maturity securities	$	2,412,308	$	763	$	(278,888	)	$	2,134,183		100.00	%

	December 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	$	2,553,246	$	25,873	$	(15,905	)	$	2,563,214		80.50	%
CMO/REMIC		602,555		1,586		(13,983	)		590,158		18.53	%
Municipal bonds		28,365		1,103		-			29,468		0.93	%
Other securities		1,083		-		-			1,083		0.04	%
Total available-for-sale securities	$	3,185,249	$	28,562	$	(29,888	)	$	3,183,923		100.00	%
Investment securities held-to-maturity:
Government agency/GSE	$	576,899	$	5,907	$	(7,312	)	$	575,494		29.95	%
Mortgage-backed securities		647,390		4,109		(6,106	)		645,393		33.61	%
CMO/REMIC		490,670		596		(5,030	)		486,236		25.48	%
Municipal bonds		211,011		4,714		(1,155	)		214,570		10.96	%
Total held-to-maturity securities	$	1,925,970	$	15,326	$	(19,603	)	$	1,921,693		100.00	%

Summary of Interest Income Earned on Investment Securities

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				Six Months Ended
	June 30,				June 30,
	2022		2021		2022		2021
	(Dollars in thousands)
Investment securities available-for-sale:
Taxable	$	16,863	$	9,226	$	29,512	$	18,194
Tax-advantaged		179		184		362		375
Total interest income from available-for-sale securities		17,042		9,410		29,874		18,569
Investment securities held-to-maturity:
Taxable		9,978		4,007		19,082		6,818
Tax-advantaged		1,736		1,123		3,295		2,252
Total interest income from held-to-maturity securities		11,714		5,130		22,377		9,070
Total interest income from investment securities	$	28,756	$	14,540	$	52,251	$	27,639

Summary of Amortized Cost and Fair Value of Debt Securities by Contractual Maturity

Mortgage-backed and CMO/REMIC securities are included in maturity categories based upon estimated average lives which incorporate estimated prepayment speeds.

	June 30, 2022
	Available-for-sale				Held-to-maturity
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
			(Dollars in thousands)
Due in one year or less	$	26,014	$	25,660	$	4,875	$	4,882
Due after one year through five years		1,059,708		995,539		606,745		556,072
Due after five years through ten years		2,654,991		2,403,349		737,884		659,288
Due after ten years		231,724		201,609		1,062,804		913,941
Total investment securities	$	3,972,437	$	3,626,157	$	2,412,308	$	2,134,183