Investment securities (Tables)

9 Months Ended

Sep. 30, 2012

Amortized Cost and Estimated Fair Value of Investment Securities

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

			Gross		Gross
	Amortized		unrealized		unrealized		Estimated
	cost		gains		losses		fair value
			(in thousands)
September 30, 2012
Investment securities available for sale:
U.S. Treasury and federal agencies	$	55,288		1,057		—	$	56,345
Obligations of states and political subdivisions		33,402		588		10		33,980
Mortgage-backed securities:
Government issued or guaranteed		3,502,237		246,190		175		3,748,252
Privately issued residential		1,198,896		4,929		148,757		1,055,068
Privately issued commercial		10,837		—		269		10,568
Collateralized debt obligations		43,294		15,147		1,240		57,201
Other debt securities		136,418		2,146		29,159		109,405
Equity securities		110,744		9,636		7,321		113,059
		5,091,116		279,693		186,931		5,183,878
Investment securities held to maturity:
Obligations of states and political subdivisions		192,621		8,848		29		201,440
Mortgage-backed securities:
Government issued or guaranteed		669,169		37,259		—		706,428
Privately issued		248,441		334		92,966		155,809
Other debt securities		11,094		—		—		11,094
		1,121,325		46,441		92,995		1,074,771
Other securities		318,801		—		—		318,801
Total	$	6,531,242		326,134		279,926	$	6,577,450
December 31, 2011
Investment securities available for sale:
U.S. Treasury and federal agencies	$	69,468		1,255		—	$	70,723
Obligations of states and political subdivisions		39,518		771		20		40,269
Mortgage-backed securities:
Government issued or guaranteed		4,344,116		177,392		275		4,521,233
Privately issued residential		1,369,371		6,373		239,488		1,136,256
Privately issued commercial		17,679		—		2,650		15,029
Collateralized debt obligations		43,834		11,154		2,488		52,500
Other debt securities		216,700		4,588		44,443		176,845
Equity securities		211,737		8,468		4,500		215,705
		6,312,423		210,001		293,864		6,228,560
Investment securities held to maturity:
Obligations of states and political subdivisions		188,680		9,141		28		197,793
Mortgage-backed securities:
Government issued or guaranteed		608,533		24,881		—		633,414
Privately issued		268,642		—		99,140		169,502
Other debt securities		11,853		—		—		11,853
		1,077,708		34,022		99,168		1,012,562
Other securities		366,886		—		—		366,886
Total	$	7,757,017		244,023		393,032	$	7,608,008

Changes in Credit Losses Associated with Debt Securities for Which Other-Than-Temporary Impairment Losses

The following table displays changes in credit losses associated with debt securities for which other-than-temporary impairment losses have been previously recognized in earnings for the three months and nine months ended September 30, 2012 and 2011:

	Three months ended September 30
	2012			2011
	(in thousands)
Beginning balance	$	264,197			298,141
Additions for credit losses not previously recognized		5,672			9,642
Reductions for increases in cash flows		—			(90	)
Reductions for realized losses		(67,926	)		(23,127	)
Ending balance	$	201,943			284,566
	Nine months ended September 30
	2012			2011
	(in thousands)
Beginning balance	$	285,399			327,912
Additions for credit losses not previously recognized		33,331			52,213
Reductions for increases in cash flows		—			(5,110	)
Reductions for realized losses		(116,787	)		(90,449	)
Ending balance	$	201,943			284,566

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

At September 30, 2012, 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	$	33,460		33,496
Due after one year through five years		42,405		43,791
Due after five years through ten years		8,611		9,409
Due after ten years		183,926		170,235
		268,402		256,931
Mortgage-backed securities available for sale		4,711,970		4,813,888
	$	4,980,372		5,070,819
Debt securities held to maturity:
Due in one year or less	$	36,459		36,660
Due after one year through five years		45,054		47,410
Due after five years through ten years		110,731		116,979
Due after ten years		11,471		11,485
		203,715		212,534
Mortgage-backed securities held to maturity		917,610		862,237
	$	1,121,325		1,074,771

Investment Securities in Continuous Unrealized Loss Position

A summary of investment securities that as of September 30, 2012 and December 31, 2011 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
			Unrealized					Unrealized
	Fair value		losses			Fair value		losses
			(in thousands)
September 30, 2012
Investment securities available for sale:
Obligations of states and political subdivisions	$	979		(6	)		685		(4	)
Mortgage-backed securities:
Government issued or guaranteed		5,838		(28	)		9,319		(147	)
Privately issued residential		81,620		(454	)		828,916		(148,303	)
Privately issued commercial		—		—			9,744		(269	)
Collateralized debt obligations		3,136		(30	)		5,842		(1,210	)
Other debt securities		—		—			93,266		(29,159	)
Equity securities		5,486		(3,820	)		1,580		(3,501	)
		97,059		(4,338	)		949,352		(182,593	)
Investment securities held to maturity:
Obligations of states and political subdivisions		2,839		(6	)		2,522		(23	)
Privately issued mortgage-backed securities		—		—			155,189		(92,966	)
		2,839		(6	)		157,711		(92,989	)
Total	$	99,898		(4,344	)		1,107,063		(275,582	)
December 31, 2011
Investment securities available for sale:
Obligations of states and political subdivisions	$	—		—			1,228		(20	)
Mortgage-backed securities:
Government issued or guaranteed		38,492		(190	)		6,017		(85	)
Privately issued residential		297,133		(14,188	)		751,077		(225,300	)
Privately issued commercial		—		—			15,029		(2,650	)
Collateralized debt obligations		2,871		(335	)		4,863		(2,153	)
Other debt securities		72,637		(9,883	)		73,635		(34,560	)
Equity securities		9,883		(4,500	)		—		—
		421,016		(29,096	)		851,849		(264,768	)
Investment securities held to maturity:
Obligations of states and political subdivisions		3,084		(4	)		1,430		(24	)
Privately issued mortgage-backed securities		1,883		(592	)		167,139		(98,548	)
		4,967		(596	)		168,569		(98,572	)
Total	$	425,983		(29,692	)		1,020,418		(363,340	)