Investment Securities Available for Sale (Tables)

12 Months Ended

Dec. 31, 2023

Summary of Available-for-Sale Investment Securities

The amortized cost, gross unrealized gains and losses, and estimated fair values of investment securities available for sale at December 31, 2023 and 2022 are summarized below.


	December 31, 2023
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
U.S. Treasury securities	$	588,082	$	9,547	$	—	$	597,629
U.S. Government agency securities	29,993		—		(1,053)		28,940
Mortgage-backed securities issued by U.S. Government agencies	1,021,612		2,037		(97,985)		925,664
Mortgage-backed securities issued by U.S. Government sponsored enterprises	7,523,399		1,192		(1,094,212)		6,430,379
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises	692,487		—		(104,892)		587,595
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises	1,226,672		18,764		(35,653)		1,209,783

Corporate debt securities and other debt securities	9,009		—		(337)		8,672
Total investment securities available for sale(1)	$	11,091,254	$	31,540	$	(1,334,132)	$	9,788,662

	December 31, 2022
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
U.S. Treasury securities	$	515,953	$	—	$	(44,140)	$	471,813
U.S. Government agency securities	52,411		—		(3,613)		48,798
Mortgage-backed securities issued by U.S. Government agencies	904,593		1,624		(113,468)		792,749
Mortgage-backed securities issued by U.S. Government sponsored enterprises	8,144,374		936		(1,250,240)		6,895,070
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises	769,498		—		(114,371)		655,127
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises	877,590		—		(71,645)		805,945

Corporate debt securities and other debt securities	8,908		—		(307)		8,601
Total investment securities available for sale(1)	$	11,273,327	$	2,560	$	(1,597,784)	$	9,678,103

(1) The amounts reported exclude accrued interest receivable on investment securities available for sale of $26.6 million and $22.7 million at December 31, 2023 and 2022, respectively, which is presented as a component of other assets on the consolidated balance sheets. See "Part II - Item 8. Financial Statements and Supplementary Data - Note 6 - Other Assets" in this Report for more information on other assets.

Schedule of Unrealized Loss on Investments

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, 2023 and 2022 are presented below.


	December 31, 2023
	Less than 12 Months				12 Months or Longer				Total
(in thousands)	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses

U.S. Government agency securities	$	—	$	—	$	28,940	$	(1,053)	$	28,940	$	(1,053)
Mortgage-backed securities issued by U.S. Government agencies	159,402		(1,268)		565,358		(96,717)		724,760		(97,985)
Mortgage-backed securities issued by U.S. Government sponsored enterprises	215,917		(1,193)		6,045,914		(1,093,019)		6,261,831		(1,094,212)
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises	—		—		587,595		(104,892)		587,595		(104,892)
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises	34,406		(205)		276,675		(35,448)		311,081		(35,653)
Corporate debt securities and other debt securities	—		—		8,672		(337)		8,672		(337)
Total	$	409,725	$	(2,666)	$	7,513,154	$	(1,331,466)	$	7,922,879	$	(1,334,132)

	December 31, 2022
	Less than 12 Months				12 Months or Longer				Total
(in thousands)	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
U.S. Treasury securities	$	139,737	$	(6,789)	$	307,582	$	(37,351)	$	447,319	$	(44,140)
U.S. Government agency securities	28,938		(1,053)		19,603		(2,560)		48,541		(3,613)
Mortgage-backed securities issued by U.S. Government agencies	187,655		(5,952)		521,395		(107,516)		709,050		(113,468)
Mortgage-backed securities issued by U.S. Government sponsored enterprises	1,473,348		(120,135)		5,365,233		(1,130,105)		6,838,581		(1,250,240)
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises	119,649		(10,311)		535,478		(104,060)		655,127		(114,371)
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises	565,382		(29,383)		240,564		(42,262)		805,946		(71,645)
Corporate debt securities and other debt securities	8,601		(307)		—		—		8,601		(307)
Total	$	2,523,310	$	(173,930)	$	6,989,855	$	(1,423,854)	$	9,513,165	$	(1,597,784)

Schedule of Amortized Cost and Estimated Fair Value by Contractual Maturity of Investment Securities Available-for-Sale

The amortized cost and fair value by contractual maturity of investment securities available for sale at December 31, 2023 are shown below. The expected life of MBSs or CMOs may differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. For purposes of the maturity table, MBSs and CMOs, which are not due at a single maturity date, have been classified based on the final contractual maturity date.


	Distribution of Maturities at December 31, 2023
(in thousands)	Within One Year		1 to 5 Years		5 to 10 Years		More Than 10 Years		Total
Amortized Cost
U.S. Treasury securities	$	25,688	$	141,378	$	421,016	$	—	$	588,082
U.S. Government agency securities	—		29,993		—		—		29,993
Mortgage-backed securities issued by U.S. Government agencies	—		65		3		1,021,544		1,021,612
Mortgage-backed securities issued by U.S. Government sponsored enterprises	—		—		11,063		7,512,336		7,523,399
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises	—		50		10,508		681,929		692,487
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises	66,599		545,350		597,302		17,421		1,226,672

Corporate debt securities and other debt securities	—		9,009		—		—		9,009
Total amortized cost	$	92,287	$	725,845	$	1,039,892	$	9,233,230	$	11,091,254

Fair Value
U.S. Treasury securities	$	25,688	$	143,641	$	428,300	$	—	$	597,629
U.S. Government agency securities	—		28,940		—		—		28,940
Mortgage-backed securities issued by U.S. Government agencies	—		63		3		925,598		925,664
Mortgage-backed securities issued by U.S. Government sponsored enterprises	—		—		10,341		6,420,038		6,430,379
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises	—		49		10,220		577,326		587,595
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises	67,822		544,620		582,238		15,103		1,209,783

Corporate debt securities and other debt securities	—		8,672		—		—		8,672
Total fair value	$	93,510	$	725,985	$	1,031,102	$	7,938,065	$	9,788,662

Summary of Sales Transactions in the Investment Securities Available-for-Sale Portfolio

Gross gains and gross losses on sales of securities available for sale for the years ended December 31, 2023, 2022, and 2021 are presented below.


(in thousands)	2023		2022		2021
Gross realized gains on sales	$	5,141	$	—	$	1,191
Gross realized losses on sales	(81,859)		—		(1,990)
Investment securities gains (losses), net	$	(76,718)	$	—	$	(799)