Investment securities (Tables)

12 Months Ended

Dec. 31, 2021

Investments Debt And Equity Securities [Abstract]

Amortized Cost and Estimated Fair Value of Investment Securities

The amortized cost and estimated fair value of investment securities were as follows:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(In thousands)
December 31, 2021
Investment securities available for sale:
U.S. Treasury and federal agencies	$	682,267	$	229	$	3,806	$	678,690
Mortgage-backed securities:
Government issued or guaranteed		3,042,771		113,102		561		3,155,312
Other debt securities		124,309		1,974		4,481		121,802
		3,849,347		115,305		8,848		3,955,804
Investment securities held to maturity:
U.S. Treasury and federal agencies		3,052		—		9		3,043
Obligations of states and political subdivisions		177		2		—		179
Mortgage-backed securities:
Government issued or guaranteed		2,667,328		49,221		8,376		2,708,173
Privately issued		61,555		10,520		14,742		57,333
Other debt securities		2,562		—		—		2,562
		2,734,674		59,743		23,127		2,771,290
Total debt securities	$	6,584,021	$	175,048	$	31,975	$	6,727,094
Equity and other securities:
Readily marketable equity — at fair value	$	73,774	$	4,460	$	594	$	77,640
Other — at cost		387,742		—		—		387,742
Total equity and other securities	$	461,516	$	4,460	$	594	$	465,382
December 31, 2020
Investment securities available for sale:
U.S. Treasury and federal agencies	$	9,154	$	198	$	14	$	9,338
Mortgage-backed securities:
Government issued or guaranteed		4,475,406		208,787		755		4,683,438
Privately issued		16		—		—		16
Other debt securities		136,451		1,664		8,301		129,814
		4,621,027		210,649		9,070		4,822,606
Investment securities held to maturity:
U.S. Treasury and federal agencies		2,999		—		—		2,999
Obligations of states and political subdivisions		1,531		9		—		1,540
Mortgage-backed securities:
Government issued or guaranteed		1,664,443		100,176		11		1,764,608
Privately issued		77,155		11,056		17,938		70,273
Other debt securities		2,861		—		—		2,861
		1,748,989		111,241		17,949		1,842,281
Total debt securities	$	6,370,016	$	321,890	$	27,019	$	6,664,887
Equity and other securities:
Readily marketable equity — at fair value	$	67,891	$	25,094	$	—	$	92,985
Other — at cost		381,117		—		—		381,117
Total equity and other securities	$	449,008	$	25,094	$	—	$	474,102

Investment Ratings of All Privately Issued Mortgage-Backed Securities and Other Debt Securities

As of December 31, 2021, the latest available investment ratings of all obligations of states and political subdivisions, privately issued mortgage-backed securities and other debt securities were:

					Average Credit Rating of Fair Value Amount
	Amortized Cost		Estimated Fair Value		A or Better		BBB		BB		B or Less		Not Rated
	(In thousands)
Obligations of states and political    subdivisions	$	177	$	179	$	179	$	—	$	—	$	—	$	—
Privately issued mortgage-backed    securities		61,555		57,333		—		—		—		485		56,848
Other debt securities		126,871		124,364		6,526		51,349		32,593		—		33,896
Total	$	188,603	$	181,876	$	6,705	$	51,349	$	32,593	$	485	$	90,744

Amortized Cost and Estimated Fair Value of Collateralized Mortgage Obligations

The amortized cost and estimated fair value of collateralized mortgage obligations included in mortgage-backed securities were as follows:

	December 31
	2021		2020
	(In thousands)
Collateralized mortgage obligations:
Amortized cost	$	61,980	$	77,964
Estimated fair value		57,763		71,099

Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity

At December 31, 2021, the amortized cost and estimated fair value of debt securities by contractual maturity were as follows:

	Amortized Cost		Estimated Fair Value
	(In thousands)
Debt securities available for sale:
Due in one year or less	$	6,912	$	6,943
Due after one year through five years		683,983		680,827
Due after five years through ten years		85,681		86,205
Due after ten years		30,000		26,517
		806,576		800,492
Mortgage-backed securities available for sale		3,042,771		3,155,312
	$	3,849,347	$	3,955,804
Debt securities held to maturity:
Due in one year or less	$	3,229	$	3,222
Due after ten years		2,562		2,562
		5,791		5,784
Mortgage-backed securities held to maturity		2,728,883		2,765,506
	$	2,734,674	$	2,771,290

Investment Securities in Continuous Unrealized Loss Position

A summary of investment securities that as of December 31, 2021 and 2020 had been in a continuous unrealized loss position for less than twelve months and those that had been in a continuous unrealized loss position for twelve months or longer follows:

	Less Than 12 Months				12 Months or More
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
	(In thousands)
December 31, 2021
Investment securities available for sale:
U.S. Treasury and federal agencies	$	598,566	$	3,806	$	—	$	—
Mortgage-backed securities:
Government issued or guaranteed		10,111		54		20,824		507
Other debt securities		3,760		74		66,419		4,407
		612,437		3,934		87,243		4,914
Investment securities held to maturity:
U.S. Treasury and federal agencies		3,043		9		—		—
Mortgage-backed securities:
Government issued or guaranteed		1,372,236		8,356		1,251		20
Privately issued		—		—		43,692		14,742
		1,375,279		8,365		44,943		14,762
Total	$	1,987,716	$	12,299	$	132,186	$	19,676
December 31, 2020
Investment securities available for sale:
U.S. Treasury and federal agencies	$	985	$	14	$	—	$	—
Mortgage-backed securities:
Government issued or guaranteed		18,687		356		16,556		399
Other debt securities		16,055		181		63,462		8,120
		35,727		551		80,018		8,519
Investment securities held to maturity:
Mortgage-backed securities:
Government issued or guaranteed		2,039		11		—		—
Privately issued		—		—		52,418		17,938
		2,039		11		52,418		17,938
Total	$	37,766	$	562	$	132,436	$	26,457