INVESTMENTS (Tables)

6 Months Ended

Jun. 30, 2022

Investments, Debt and Equity Securities [Abstract]

Debt Securities, Available-for-sale

The following tables detail the amortized cost, allowance for credit losses and the estimated fair value of the Company's investments in available-for-sale and held-to-maturity debt securities. None of the Company's investments in debt securities are classified as trading.

	June 30, 2022
(Dollars in thousands)	Amortized Cost		Gross Unrealized  Gain		Gross Unrealized  Loss		Allowance for Credit Losses		Fair Value
Available-for-Sale Debt Securities
Collateralized mortgage obligation (CMO)	$	624,579	$	64	$	66,988	$	—	$	557,655
Fannie Mae (FNMA) mortgage-backed securities (MBS)	3,997,394		1,473		406,409		—		3,592,458
Freddie Mac (FHLMC) MBS	123,756		25		7,385		—		116,396
Ginnie Mae (GNMA) MBS	41,078		21		1,938		—		39,161
Government-sponsored enterprises (GSE) agency notes	229,296		—		38,879		—		190,417
	$	5,016,103	$	1,583	$	521,599	$	—	$	4,496,087
Held-to-Maturity Debt Securities(1)
FNMA MBS	$	931,421	$	—	$	—	$	—	$	931,421
State and political subdivisions	132,267		322		1,151		6		131,432
Foreign bonds	500		—		1		—		499
	$	1,064,188	$	322	$	1,152	$	6	$	1,063,352

(1)Held-to-maturity securities transferred from available-for-sale are included in held-to-maturity at fair value basis at the time of transfer. The amortized cost of transferred held-to-maturity securities included net unrealized losses of $157.4 million at June 30, 2022, which are offset in Accumulated other comprehensive (loss) income. At the time of transfer, there was no allowance for credit loss on the available-for-sale securities. Subsequent to transfer, the securities were evaluated for credit loss.

	December 31, 2021
(Dollars in thousands)	Amortized Cost		Gross Unrealized  Gain		Gross Unrealized  Loss		Allowance for Credit Losses		Fair Value
Available-for-Sale Debt Securities
CMO	$	586,830	$	3,569	$	14,633	$	—	$	575,766
FNMA MBS	4,275,307		24,170		53,793		—		4,245,684
FHLMC MBS	139,708		6,336		516		—		145,528
GNMA MBS	17,456		551		71		—		17,936
GSE agency notes	230,581		—		10,184		—		220,397
	$	5,249,882	$	34,626	$	79,197	$	—	$	5,205,311
Held-to-Maturity Debt Securities(1)
State and political subdivisions	$	90,146	$	3,489	$	—	$	4	$	93,631
Foreign bonds	500		—		—		—		500
	$	90,646	$	3,489	$	—	$	4	$	94,131

(1)Held-to–maturity securities transferred from available-for-sale are included in held-to-maturity at fair value at the time of transfer. The amortized cost of transferred held-to-maturity securities included net unrealized gains of $0.2 million at December 31, 2021, which are offset in Accumulated other comprehensive income. At the time of transfer, there was no allowance for credit loss on the available-for-sale securities. Subsequent to transfer, the securities were evaluated for credit loss.

Debt Securities, Held-to-maturity

The following tables detail the amortized cost, allowance for credit losses and the estimated fair value of the Company's investments in available-for-sale and held-to-maturity debt securities. None of the Company's investments in debt securities are classified as trading.

	June 30, 2022
(Dollars in thousands)	Amortized Cost		Gross Unrealized  Gain		Gross Unrealized  Loss		Allowance for Credit Losses		Fair Value
Available-for-Sale Debt Securities
Collateralized mortgage obligation (CMO)	$	624,579	$	64	$	66,988	$	—	$	557,655
Fannie Mae (FNMA) mortgage-backed securities (MBS)	3,997,394		1,473		406,409		—		3,592,458
Freddie Mac (FHLMC) MBS	123,756		25		7,385		—		116,396
Ginnie Mae (GNMA) MBS	41,078		21		1,938		—		39,161
Government-sponsored enterprises (GSE) agency notes	229,296		—		38,879		—		190,417
	$	5,016,103	$	1,583	$	521,599	$	—	$	4,496,087
Held-to-Maturity Debt Securities(1)
FNMA MBS	$	931,421	$	—	$	—	$	—	$	931,421
State and political subdivisions	132,267		322		1,151		6		131,432
Foreign bonds	500		—		1		—		499
	$	1,064,188	$	322	$	1,152	$	6	$	1,063,352

(1)Held-to-maturity securities transferred from available-for-sale are included in held-to-maturity at fair value basis at the time of transfer. The amortized cost of transferred held-to-maturity securities included net unrealized losses of $157.4 million at June 30, 2022, which are offset in Accumulated other comprehensive (loss) income. At the time of transfer, there was no allowance for credit loss on the available-for-sale securities. Subsequent to transfer, the securities were evaluated for credit loss.

	December 31, 2021
(Dollars in thousands)	Amortized Cost		Gross Unrealized  Gain		Gross Unrealized  Loss		Allowance for Credit Losses		Fair Value
Available-for-Sale Debt Securities
CMO	$	586,830	$	3,569	$	14,633	$	—	$	575,766
FNMA MBS	4,275,307		24,170		53,793		—		4,245,684
FHLMC MBS	139,708		6,336		516		—		145,528
GNMA MBS	17,456		551		71		—		17,936
GSE agency notes	230,581		—		10,184		—		220,397
	$	5,249,882	$	34,626	$	79,197	$	—	$	5,205,311
Held-to-Maturity Debt Securities(1)
State and political subdivisions	$	90,146	$	3,489	$	—	$	4	$	93,631
Foreign bonds	500		—		—		—		500
	$	90,646	$	3,489	$	—	$	4	$	94,131

(1)Held-to–maturity securities transferred from available-for-sale are included in held-to-maturity at fair value at the time of transfer. The amortized cost of transferred held-to-maturity securities included net unrealized gains of $0.2 million at December 31, 2021, which are offset in Accumulated other comprehensive income. At the time of transfer, there was no allowance for credit loss on the available-for-sale securities. Subsequent to transfer, the securities were evaluated for credit loss.

The following table presents the activity in the allowance for credit losses for state and political subdivisions debt securities for the three and six months ended June 30, 2022 and 2021:

	Three months ended June 30,				Six months ended June 30,
(Dollars in thousands)	2022		2021		2022		2021
Allowance for credit losses:
Beginning balance	$	4	$	5	$	4	$	6
Provision for credit losses	2		—		2		(1)
Ending balance	$	6	$	5	$	6	$	5

Schedule of Maturities of Investment Securities Available-for-Sale and Held-to-Maturity

The scheduled maturities of available-for-sale debt securities at June 30, 2022 and December 31, 2021 are presented in the table below:

	Available-for-Sale
	Amortized		Fair
(Dollars in thousands)	Cost		Value
June 30, 2022 (1)
Within one year	$	1,890	$	1,888
After one year but within five years	98,602		95,371
After five years but within ten years	361,217		329,345
After ten years	4,554,394		4,069,483
	$	5,016,103	$	4,496,087
December 31, 2021 (1)
Within one year	$	—	$	—
After one year but within five years	103,960		107,009
After five years but within ten years	204,186		204,289
After ten years	4,941,736		4,894,013
	$	5,249,882	$	5,205,311

(1)Actual maturities could differ from contractual maturities.

The scheduled maturities of held-to-maturity debt securities at June 30, 2022 and December 31, 2021 are presented in the table below:

	Held-to-Maturity
	Amortized		Fair
(Dollars in thousands)	Cost		Value
June 30, 2022 (1)
Within one year	$	731	$	730
After one year but within five years	5,567		5,580
After five years but within ten years	40,830		40,830
After ten years	1,017,060		1,016,212
	$	1,064,188	$	1,063,352
December 31, 2021 (1)
Within one year	$	232	$	234
After one year but within five years	2,675		2,736
After five years but within ten years	44,137		45,404
After ten years	43,602		45,757
	$	90,646	$	94,131

(1)Actual maturities could differ from contractual maturities.

Schedule of Investment Securities' Gross Unrealized Losses and Fair Value by Investment Category

For debt securities in an unrealized loss position and an allowance has not been recorded, the table below shows the gross unrealized losses and fair value by investment category and length of time that individual debt securities were in a continuous unrealized loss position at June 30, 2022.

	Duration of Unrealized Loss Position
	Less than 12 months				12 months or longer				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(Dollars in thousands)	Value		Loss		Value		Loss		Value		Loss
Available-for-sale debt securities:
CMO	$	375,687	$	32,423	$	167,328	$	34,565	$	543,015	$	66,988
FNMA MBS	3,083,263		334,083		421,083		72,326		3,504,346		406,409
FHLMC MBS	104,590		5,638		8,718		1,747		113,308		7,385
GNMA MBS	36,513		1,626		1,880		312		38,393		1,938
GSE agency notes	36,484		6,455		153,933		32,424		190,417		38,879
	$	3,636,537	$	380,225	$	752,942	$	141,374	$	4,389,479	$	521,599
Held-to-maturity debt securities:
FNMA MBS	$	751,546	$	122,546	$	179,874	$	35,044	$	931,420	$	157,590

For debt securities in an unrealized loss position, the table below shows the gross unrealized losses and fair value by investment category and length of time that individual debt securities were in a continuous unrealized loss position at December 31, 2021.

	Duration of Unrealized Loss Position
	Less than 12 months				12 months or longer				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(Dollars in thousands)	Value		Loss		Value		Loss		Value		Loss
Available-for-sale debt securities:
CMO	$	411,347	$	12,730	$	35,638	$	1,903	$	446,985	$	14,633
FNMA MBS	3,018,606		41,021		356,665		12,772		3,375,271		53,793
FHLMC MBS	11,227		348		1,917		168		13,144		516
GNMA MBS	4,847		71		—		—		4,847		71
GSE agency notes	64,509		1,918		155,888		8,266		220,397		10,184
	$	3,510,536	$	56,088	$	550,108	$	23,109	$	4,060,644	$	79,197

Held-to-Maturity, Credit Quality Indicator

The following table summarizes the amortized cost of debt securities held-to-maturity as of June 30, 2022, aggregated by credit quality indicator:

(Dollars in thousands)	FNMA MBS		State and political subdivisions		Foreign bonds
A+ rated or higher	$	—	$	132,267	$	500
Not rated	931,421		—		—
Ending balance	$	931,421	$	132,267	$	500

The following table summarizes the amortized cost of debt securities held-to-maturity as of December 31, 2021, aggregated by credit quality indicator:

(Dollars in thousands)	State and political subdivisions		Foreign bonds
A+ rated or higher	$	90,146	$	500
Not rated	—		—
Ending balance	$	90,146	$	500