Securities (Tables)

6 Months Ended

Jun. 30, 2021

Investments, Debt and Equity Securities [Abstract]

Summary of Amortized Cost and Fair Value of Available-for-sale and Held-to-maturity Securities

The amortized cost and fair value of securities available-for-sale and held-to-maturity at June 30, 2021 and December 31, 2020 are summarized as follows (in thousands):


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
June 30, 2021:
Securities available-for-sale:
U.S. Treasury securities	$	111,475	$	5	$	11	$	111,469
U.S. government agency securities	421,833		3,214		2,191		422,856
Mortgage-backed securities	1,854,519		50,747		6,018		1,899,248
State and municipal securities	1,535,461		48,999		3,747		1,580,713
Asset-backed securities	200,200		318		430		200,088
Corporate notes and other	114,878		3,422		1,604		116,696
	$	4,238,366	$	106,705	$	14,001	$	4,331,070
Securities held-to-maturity:
State and municipal securities	$	996,036	$	35,035	$	432	$	1,030,639
	$	996,036	$	35,035	$	432	$	1,030,639
Allowance for credit losses - securities held-to-maturity	(198)
Securities held-to-maturity, net of allowance for credit losses	$	995,838


December 31, 2020:
Securities available-for-sale:
U.S. Treasury securities	$	82,199	$	10	$	—	$	82,209
U.S. government agency securities	74,916		1,547		60		76,403
Mortgage-backed securities	1,623,759		67,759		2,327		1,689,191
State and municipal securities	1,411,288		44,559		12,484		1,443,363
Asset-backed securities	177,878		715		657		177,936
Corporate notes and other	117,256		2,632		2,309		117,579
	$	3,487,296	$	117,222	17,837		$	3,586,681
Securities held-to-maturity:
State and municipal securities	$	1,028,550	$	38,272	$	291	$	1,066,531
	$	1,028,550	$	38,272	$	291	$	1,066,531
Allowance for credit losses - securities held-to-maturity	(191)
Securities held-to-maturity, net of allowance for credit losses	$	1,028,359

Amortized Cost and Fair Value of Debt Securities by Contractual Maturity

The amortized cost and fair value of debt securities as of June 30, 2021 by contractual maturity are shown below. Actual maturities may differ from contractual maturities of mortgage- and asset-backed securities since the mortgages and assets underlying the securities may be called or prepaid with or without penalty. Therefore, these securities are not included in the maturity categories in the following summary (in thousands):


	Available-for-sale				Held-to-maturity
June 30, 2021:	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due in one year or less	$	112,691	$	112,686	$	—	$	—
Due in one year to five years	33,685		33,706		1,409		1,470
Due in five years to ten years	496,477		508,583		6,609		6,704
Due after ten years	1,540,794		1,576,759		988,018		1,022,465
Mortgage-backed securities	1,854,519		1,899,248		—		—
Asset-backed securities	200,200		200,088		—		—
	$	4,238,366	$	4,331,070	$	996,036	$	1,030,639

Classification of Investments According to Term of Unrealized Losses of Less than Twelve Months or Twelve Months or Longer

At June 30, 2021 and December 31, 2020, the following investments had unrealized losses. The table below classifies these investments according to the term of the unrealized losses of less than twelve months or twelve months or longer (in thousands):


	Investments with an Unrealized Loss of less than 12 months				Investments with an Unrealized Loss of 12 months or longer				Total Investments with an Unrealized Loss
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
At June 30, 2021
U.S. Treasury securities	$	59,973	$	11	$	—	$	—	$	59,973	$	11
U.S. government agency securities	111,928		2,172		5,497		19		117,425		2,191
Mortgage-backed securities	361,860		5,059		54,747		959		416,607		6,018
State and municipal securities	117,715		1,035		167,184		2,712		284,899		3,747
Asset-backed securities	85,178		285		6,859		145		92,037		430
Corporate notes	4,990		10		24,813		1,594		29,803		1,604
Total temporarily-impaired securities	$	741,644	$	8,572	$	259,100	$	5,429	$	1,000,744	$	14,001

At December 31, 2020
U.S. Treasury securities	$	—	$	—	$	—	$	—	$	—	$	—
U.S. government agency securities	9,962		38		6,091		22		16,053		60
Mortgage-backed securities	165,696		1,772		35,997		555		201,693		2,327
State and municipal securities	175,115		2,220		345,435		10,264		520,550		12,484
Asset-backed securities	46,399		207		52,840		450		99,239		657
Corporate notes	9,978		40		23,920		2,269		33,898		2,309
Total temporarily-impaired securities	$	407,150	$	4,277	$	464,283	$	13,560	$	871,433	$	17,837