Investment Securities (Tables)

12 Months Ended

Dec. 31, 2023

Dec. 31, 2019

Investments, Debt and Equity Securities [Abstract]

Amortized Cost, Unrealized Gains And Losses, And Fair Value Of Investment Securities

The following tables present the amortized cost, unrealized gains, unrealized losses, and approximate fair values of debt securities as of December 31, 2023 and 2022: 

	December 31, 2023
(in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Available for sale:
U.S. Treasury and agencies	$	1,551,074	$	6,192	$	(78,874)	$	1,478,392
Obligations of states and political subdivisions	1,073,264		20,451		(21,610)		1,072,105
Mortgage-backed securities and collateralized mortgage obligations	6,638,439		28,558		(387,624)		6,279,373
Total available for sale securities	$	9,262,777	$	55,201	$	(488,108)	$	8,829,870
Held to maturity:
Mortgage-backed securities and collateralized mortgage obligations	$	2,300	$	725	$	—	$	3,025
Total held to maturity securities	$	2,300	$	725	$	—	$	3,025

	December 31, 2022
(in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Available for sale:
U.S. Treasury and agencies	$	1,035,532	$	—	$	(99,358)	$	936,174
Obligations of states and political subdivisions	297,610		231		(28,041)		269,800
Mortgage-backed securities and collateralized mortgage obligations	2,405,139		3		(414,950)		1,990,192
Total available for sale securities	$	3,738,281	$	234	$	(542,349)	$	3,196,166
Held to maturity:
Mortgage-backed securities and collateralized mortgage obligations	$	2,476	$	721	$	—	$	3,197
Total held to maturity securities	$	2,476	$	721	$	—	$	3,197

Debt Securities, Available-for-Sale

Debt securities that were in an unrealized loss position as of December 31, 2023 and 2022 are presented in the following tables, based on the length of time individual securities have been in an unrealized loss position.

	December 31, 2023
	Less than 12 Months				12 Months or Longer				Total
(in thousands)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Available for sale:
U.S. Treasury and agencies	$	99,898	$	(1,074)	$	822,245	$	(77,800)	$	922,143	$	(78,874)
Obligations of states and political subdivisions	103,256		(580)		169,231		(21,030)		272,487		(21,610)
Mortgage-backed securities and collateralized mortgage obligations	1,089,640		(10,355)		1,817,768		(377,269)		2,907,408		(387,624)
Total temporarily impaired securities	$	1,292,794	$	(12,009)	$	2,809,244	$	(476,099)	$	4,102,038	$	(488,108)

	December 31, 2022
	Less than 12 Months				12 Months or Longer				Total
(in thousands)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Available for sale:
U.S. Treasury and agencies	$	734,473	$	(71,967)	$	201,701	$	(27,391)	$	936,174	$	(99,358)
Obligations of states and political subdivisions	160,078		(10,037)		60,381		(18,004)		220,459		(28,041)
Mortgage-backed securities and collateralized mortgage obligations	592,032		(61,813)		1,398,061		(353,137)		1,990,093		(414,950)
Total temporarily impaired securities	$	1,486,583	$	(143,817)	$	1,660,143	$	(398,532)	$	3,146,726	$	(542,349)

Schedule Of Maturities Of Investment Securities

The following table presents the contractual maturities of debt securities as of December 31, 2023:

	Available For Sale				Held To Maturity
(in thousands)	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due within one year	$	71,438	$	70,451	$	—	$	—
Due after one year through five years	2,127,299		2,106,753		2		2
Due after five years through ten years	2,388,442		2,323,581		3		67
Due after ten years	4,675,598		4,329,085		2,295		2,956
Total debt securities	$	9,262,777	$	8,829,870	$	2,300	$	3,025

Investment Securities Pledged To Secure Borrowings And Public Deposits

The following table presents, as of December 31, 2023, investment securities which were pledged to secure borrowings, public deposits, and repurchase agreements as permitted or required by law: 

(in thousands)	Amortized Cost		Fair Value
To state and local governments to secure public deposits	$	1,796,582	$	1,657,160
To secure repurchase agreements	386,989		358,162
Other securities pledged	1,863,025		1,766,958
Total pledged securities	$	4,046,596	$	3,782,280