Investment Securities (Tables)

12 Months Ended

Dec. 31, 2023

Summary of Amortized Cost and Estimated Fair Values of Available for Sale Securities

The amortized cost and estimated fair values of securities available for sale are summarized as follows.

	December 31, 2023
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Allowance For Credit Losses		Estimated Fair Value
U.S. Treasury securities and obligations of U.S. Government corporations and agencies	$	492,638	$	4	$	7,692	$	0	$	484,950
State and political subdivisions		613,588		11		79,768		0		533,831
Residential mortgage-backed securities
Agency		1,217,744		7		167,810		0		1,049,941
Non-agency		100,364		0		9,753		0		90,611
Commercial mortgage-backed securities
Agency		511,560		13		52,275		0		459,298
Asset-backed securities		872,048		44		11,454		0		860,638
Single issue trust preferred securities		16,380		0		1,239		0		15,141
Other corporate securities		325,573		0		33,606		0		291,967
Total	$	4,149,895	$	79	$	363,597	$	0	$	3,786,377

	December 31, 2022
(Dollars in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Allowance For Credit Losses		Estimated Fair Value
U.S. Treasury securities and obligations of U.S. Government corporations and agencies	$	548,407	$	12	$	18,927	$	0	$	529,492
State and political subdivisions		820,167		36		110,673		0		709,530
Residential mortgage-backed securities
Agency		1,369,471		4		194,531		0		1,174,944
Non-agency		121,336		66		9,429		0		111,973
Commercial mortgage-backed securities
Agency		627,768		8		65,223		0		562,553
Asset-backed securities		943,813		0		32,202		0		911,611
Single issue trust preferred securities		17,342		88		1,146		0		16,284
Other corporate securities		563,425		44		37,931		0		525,538
Total	$	5,011,729	$	258	$	470,062	$	0	$	4,541,925

Summary of Securities Available for Sale in an Unrealized Loss Position

The following is a summary of securities available for sale which were in an unrealized loss position at December 31, 2023 and December 31, 2022.

	Less than 12 months				12 months or longer				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(Dollars in thousands)	Value		Losses		Value		Losses		Value		Losses
December 31, 2023
U.S. Treasury securities and obligations of U.S. Government corporations and agencies	$	4,625	$	11	$	477,615	$	7,681	$	482,240	$	7,692
State and political subdivisions		2,050		193		517,186		79,575		519,236		79,768
Residential mortgage-backed securities
Agency		9,755		51		1,038,632		167,759		1,048,387		167,810
Non-agency		8,964		101		81,647		9,652		90,611		9,753
Commercial mortgage-backed securities
Agency		0		0		456,866		52,275		456,866		52,275
Asset-backed securities		15,866		216		829,778		11,238		845,644		11,454
Single issue trust preferred securities		2,922		182		12,219		1,057		15,141		1,239
Other corporate securities		0		0		274,308		33,606		274,308		33,606
Total	$	44,182	$	754	$	3,688,251	$	362,843	$	3,732,433	$	363,597

	Less than 12 months				12 months or longer				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(Dollars in thousands)	Value		Losses		Value		Losses		Value		Losses
December 31, 2022
U.S. Treasury securities and obligations of U.S. Government corporations and agencies	$	473,025	$	13,628	$	48,793	$	5,299	$	521,818	$	18,927
State and political subdivisions		496,328		63,019		192,234		47,654		688,562		110,673
Residential mortgage-backed securities
Agency		623,587		70,744		550,135		123,787		1,173,722		194,531
Non-agency		58,839		2,083		42,901		7,346		101,740		9,429
Commercial mortgage-backed securities
Agency		396,380		27,469		163,226		37,754		559,606		65,223
Asset-backed securities		425,482		14,134		486,129		18,068		911,611		32,202
Single issue trust preferred securities		0		0		13,109		1,146		13,109		1,146
Other corporate securities		195,425		18,064		261,170		19,867		456,595		37,931
Total	$	2,669,066	$	209,141	$	1,757,697	$	260,921	$	4,426,763	$	470,062

Summary of Gains or Losses on Proceeds from Maturities, Sales and Calls of Available for Sale Securities by Specific Identification Method

	Year Ended
(In thousands)	2023		2022		2021
Proceeds from maturities, sales and calls	$	952,213	$	575,748	$	731,902
Gross realized gains		0		2		1,673
Gross realized losses		7,659		0		122

Summary of Maturities of Debt Securities Held to Maturity by Amortized Cost and Estimated Fair Value

(In thousands)	Amortized Cost		Estimated Fair Value
Due in one year or less	$	497,555	$	493,651
Due after one year through five years		448,020		416,436
Due after five years through ten years		852,698		751,780
Due after ten years		2,351,622		2,124,510
Total	$	4,149,895	$	3,786,377

Summary of Equity Securities

	Year Ended
(In thousands)	December 31, 2023			December 31, 2022
Net gains recognized during the period on equity securities sold	$	0		$	0
Unrealized gains recognized during the period on equity securities still held at period end		358			94
Unrealized losses recognized during the period on equity securities still held at period end		(345	)		(684	)
Net gains (losses) recognized during the period	$	13		$	(590	)