Investment Securities

3 Months Ended

Mar. 31, 2021

Investments, Debt and Equity Securities [Abstract]

The following tables present the amortized cost, unrealized gains, unrealized losses and approximate fair values of debt securities at March 31, 2021 and December 31, 2020:


	March 31, 2021
(in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Available for sale:
U.S. Treasury and agencies	$	708,821	$	30,012	$	(2,175)	$	736,658
Obligations of states and political subdivisions	263,457		12,698		(1,075)		275,080
Residential mortgage-backed securities and collateralized mortgage obligations	2,151,838		39,390		(35,141)		2,156,087

Total available for sale securities	$	3,124,116	$	82,100	$	(38,391)	$	3,167,825
Held to maturity:

Residential mortgage-backed securities and collateralized mortgage obligations	$	2,954	$	842	$	—	$	3,796

Total held to maturity securities	$	2,954	$	842	$	—	$	3,796


	December 31, 2020
(in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Available for sale:
U.S. Treasury and agencies	$	698,243	$	64,271	$	(312)	$	762,202
Obligations of states and political subdivisions	263,546		15,996		(31)		279,511
Residential mortgage-backed securities and collateralized mortgage obligations	1,839,711		51,583		(449)		1,890,845

Total available for sale securities	$	2,801,500	$	131,850	$	(792)	$	2,932,558
Held to maturity:

Residential mortgage-backed securities and collateralized mortgage obligations	$	3,034	$	849	$	—	$	3,883

Total held to maturity securities	$	3,034	$	849	$	—	$	3,883

The Company elected to exclude accrued interest receivable from the amortized cost basis of debt securities disclosed throughout this note. Interest accrued on investment securities totaled $11.5 million and $8.9 million as of March 31, 2021 and December 31, 2020, respectively, and is included in Other Assets.

Debt securities that were in an unrealized loss position as of March 31, 2021 and December 31, 2020 are presented in the following tables, based on the length of time individual securities have been in an unrealized loss position.


	March 31, 2021
	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	$	39,094	$	2,175	$	—	$	—	$	39,094	$	2,175
Obligations of states and political subdivisions	38,507		1,075		—		—		38,507		1,075
Residential mortgage-backed securities and collateralized mortgage obligations	1,023,075		35,141		—		—		1,023,075		35,141
Total temporarily impaired securities	$	1,100,676	$	38,391	$	—	$	—	$	1,100,676	$	38,391


	December 31, 2020
	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	$	29,493	$	312	$	—	$	—	$	29,493	$	312
Obligations of states and political subdivisions	4,357		31		—		—		4,357		31
Residential mortgage-backed securities and collateralized mortgage obligations	215,165		449		—		—		215,165		449

Total temporarily impaired securities	$	249,015	$	792	$	—	$	—	$	249,015	$	792

These unrealized losses on the Company's debt securities were caused by changes in market interest rates or the widening of market spreads subsequent to the initial purchase of these securities and are not due to the underlying credit of the issuers. Management monitors the published credit ratings of the Company's debt securities for material rating or outlook changes. Substantially all of the Company's obligations of states and political subdivisions are general obligation issuances. All of the available for sale residential mortgage-backed securities and collateralized mortgage obligations portfolio in an unrealized loss position at March 31, 2021 are issued or guaranteed by government sponsored enterprises. Because the decline in fair value of the Company's debt securities is attributable to changes in interest rates or widening market spreads and not credit quality, these investments do not have an allowance for credit losses at March 31, 2021.

The following table presents the contractual maturities of debt securities at March 31, 2021:


	Available For Sale				Held To Maturity
(in thousands)	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due within one year	$	7,639	$	7,695	$	—	$	—
Due after one year through five years	76,491		79,415		3		3
Due after five years through ten years	891,005		927,102		9		9
Due after ten years	2,148,981		2,153,613		2,942		3,784
Total securities	$	3,124,116	$	3,167,825	$	2,954	$	3,796

The following table presents, as of March 31, 2021, investment securities that 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	$	253,107	$	262,336
Other securities pledged principally to secure repurchase agreements	599,137		621,582
Total pledged securities	$	852,244	$	883,918