Investment securities (Tables)

6 Months Ended

Jun. 30, 2018

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)
June 30, 2018
Investment securities available for sale:
U.S. Treasury and federal agencies	$	1,726,242		4		18,425	$	1,707,821
Obligations of states and political subdivisions		1,914		12		1		1,925
Mortgage-backed securities:
Government issued or guaranteed		8,046,603		15,521		244,825		7,817,299
Privately issued		26		—		2		24
Other debt securities		137,375		2,225		7,823		131,777
		9,912,160		17,762		271,076		9,658,846
Investment securities held to maturity:
Obligations of states and political subdivisions		13,547		57		20		13,584
Mortgage-backed securities:
Government issued or guaranteed		2,960,045		4,539		71,183		2,893,401
Privately issued		122,906		11,451		23,610		110,747
Other debt securities		4,597		—		—		4,597
		3,101,095		16,047		94,813		3,022,329
Total debt securities	$	13,013,255		33,809		365,889	$	12,681,175
Equity and other securities:
Readily marketable equity — at fair value		70,810		16,527		855		86,482
Other — at cost		436,579		—		—		436,579
Total equity and other securities	$	507,389		16,527		855	$	523,061

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(In thousands)
December 31, 2017
Investment securities available for sale:
U.S. Treasury and federal agencies	$	1,965,665		—		18,178	$	1,947,487
Obligations of states and political subdivisions		2,555		36		2		2,589
Mortgage-backed securities:
Government issued or guaranteed		8,755,482		59,497		98,587		8,716,392
Privately issued		28		—		—		28
Other debt securities		136,905		2,402		10,475		128,832
Equity securities		78,161		23,219		424		100,956
		10,938,796		85,154		127,666		10,896,284
Investment securities held to maturity:
Obligations of states and political subdivisions		24,562		109		49		24,622
Mortgage-backed securities:
Government issued or guaranteed		3,187,953		27,236		13,746		3,201,443
Privately issued		135,688		2,574		27,575		110,687
Other debt securities		5,010		—		—		5,010
		3,353,213		29,919		41,370		3,341,762
Other securities — at cost		415,028		—		—		415,028
Total	$	14,707,037		115,073		169,036	$	14,653,074

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

At June 30, 2018, 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	$	1,297,040		1,286,504
Due after one year through five years		436,548		428,617
Due after five years through ten years		96,521		95,992
Due after ten years		35,422		30,410
		1,865,531		1,841,523
Mortgage-backed securities available for sale		8,046,629		7,817,323
	$	9,912,160		9,658,846
Debt securities held to maturity:
Due in one year or less	$	7,630		7,633
Due after one year through five years		5,917		5,951
Due after ten years		4,597		4,597
		18,144		18,181
Mortgage-backed securities held to maturity		3,082,951		3,004,148
	$	3,101,095		3,022,329

Investment Securities in Continuous Unrealized Loss Position

A summary of investment securities that as of June 30, 2018 and December 31, 2017 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)
June 30, 2018
Investment securities available for sale:
U.S. Treasury and federal agencies	$	164,931		(1,622	)		1,539,796		(16,803	)
Obligations of states and political subdivisions		—		—			375		(1	)
Mortgage-backed securities:
Government issued or guaranteed		3,872,321		(91,083	)		2,907,972		(153,742	)
Privately issued		8		(2	)		—		—
Other debt securities		4,323		(94	)		63,902		(7,729	)
		4,041,583		(92,801	)		4,512,045		(178,275	)
Investment securities held to maturity:
Obligations of states and political subdivisions		—		—			4,218		(20	)
Mortgage-backed securities:
Government issued or guaranteed		2,252,672		(58,405	)		250,341		(12,778	)
Privately issued		—		—			53,579		(23,610	)
		2,252,672		(58,405	)		308,138		(36,408	)
Total	$	6,294,255		(151,206	)		4,820,183		(214,683	)
December 31, 2017
Investment securities available for sale:
U.S. Treasury and federal agencies	$	278,132		(1,761	)		1,669,355		(16,417	)
Obligations of states and political subdivisions		—		—			474		(2	)
Mortgage-backed securities:
Government issued or guaranteed		2,106,142		(13,695	)		3,138,841		(84,892	)
Other debt securities		3,067		(26	)		61,159		(10,449	)
Equity securities (a)		—		—			18,162		(424	)
		2,387,341		(15,482	)		4,887,991		(112,184	)
Investment securities held to maturity:
Obligations of states and political subdivisions		2,954		(4	)		6,110		(45	)
Mortgage-backed securities:
Government issued or guaranteed		1,331,759		(7,036	)		265,695		(6,710	)
Privately issued		5,061		(1,216	)		55,255		(26,359	)
		1,339,774		(8,256	)		327,060		(33,114	)
Total	$	3,727,115		(23,738	)		5,215,051		(145,298	)

(a) Beginning January 1, 2018, equity securities with readily determinable fair values are required to be measured at fair value with changes in fair value recognized in the consolidated statement of income. As a result, subsequent to December 31, 2017 disclosing the time period for which these equity securities had been in a continuous unrealized loss position is no longer relevant.