Investment securities (Tables)

3 Months Ended

Mar. 31, 2013

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)
March 31, 2013
Investment securities available for sale:
U.S. Treasury and federal agencies	$	38,907		793		—	$	39,700
Obligations of states and political subdivisions		19,545		503		7		20,041
Mortgage-backed securities:
Government issued or guaranteed		2,855,716		174,372		178		3,029,910
Privately issued residential		1,077,879		5,799		97,989		985,689
Privately issued commercial		6,414		1,144		—		7,558
Collateralized debt obligations		42,957		19,799		1,038		61,718
Other debt securities		136,645		2,371		21,505		117,511
Equity securities		110,931		27,691		7		138,615
		4,288,994		232,472		120,724		4,400,742
Investment securities held to maturity:
Obligations of states and political subdivisions		180,458		7,003		31		187,430
Mortgage-backed securities:
Government issued or guaranteed		532,074		26,003		—		558,077
Privately issued		236,632		47		81,438		155,241
Other debt securities		10,035		—		—		10,035
		959,199		33,053		81,469		910,783
Other securities		300,890		—		—		300,890
Total	$	5,549,083		265,525		202,193	$	5,612,415

	Amortized cost		Gross unrealized gains		Gross unrealized losses		Estimated fair value
December 31, 2012
Investment securities available for sale:
U.S. Treasury and federal agencies	$	38,422		922		—	$	39,344
Obligations of states and political subdivisions		20,375		534		8		20,901
Mortgage-backed securities:
Government issued or guaranteed		3,163,210		208,060		229		3,371,041
Privately issued residential		1,133,639		4,894		125,647		1,012,886
Privately issued commercial		8,648		2,378		26		11,000
Collateralized debt obligations		43,228		19,663		1,022		61,869
Other debt securities		136,603		2,247		26,900		111,950
Equity securities		98,945		14,921		3,420		110,446
		4,643,070		253,619		157,252		4,739,437
Investment securities held to maturity:
Obligations of states and political subdivisions		182,103		7,647		27		189,723
Mortgage-backed securities:
Government issued or guaranteed		597,340		31,727		—		629,067
Privately issued		242,378		160		94,900		147,638
Other debt securities		10,455		—		—		10,455
		1,032,276		39,534		94,927		976,883
Other securities		302,648		—		—		302,648
Total	$	5,977,994		293,153		252,179	$	6,018,968

Changes in Credit Losses Associated with Debt Securities for Which OTTI Losses

Changes in credit losses associated with debt securities for which OTTI losses have been recognized in earnings for the three months ended March 31, 2013 and 2012 follows:

	Three months ended March 31
	2013			2012
	(in thousands)
Beginning balance	$	197,809			285,399
Additions for credit losses not previously recognized		9,800			11,486
Reductions for realized losses		(20,495	)		(29,412	)
Ending balance	$	187,114			267,473

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

At March 31, 2013, 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	$	24,442		24,602
Due after one year through five years		22,459		23,522
Due after five years through ten years		9,221		9,843
Due after ten years		181,932		181,003
		238,054		238,970
Mortgage-backed securities available for sale		3,940,009		4,023,157
	$	4,178,063		4,262,127
Debt securities held to maturity:
Due in one year or less	$	25,558		25,691
Due after one year through five years		55,547		57,974
Due after five years through ten years		99,177		103,589
Due after ten years		10,211		10,211
		190,493		197,465
Mortgage-backed securities held to maturity		768,706		713,318
	$	959,199		910,783

Investment Securities in Continuous Unrealized Loss Position

A summary of investment securities that as of March 31, 2013 and December 31, 2012 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)
March 31, 2013
Investment securities available for sale:
Obligations of states and political subdivisions	$	572		(3	)		680		(4	)
Mortgage-backed securities:
Government issued or guaranteed		7,966		(41	)		7,450		(137	)
Privately issued		89,046		(401	)		695,871		(97,588	)
Collateralized debt obligations		—		—			6,039		(1,038	)
Other debt securities		—		—			101,198		(21,505	)
Equity securities		7		(7	)		—		—
		97,591		(452	)		811,238		(120,272	)
Investment securities held to maturity:
Obligations of states and political subdivisions		1,065		(7	)		1,794		(24	)
Privately issued mortgage-backed securities		—		—			155,050		(81,438	)
		1,065		(7	)		156,844		(81,462	)
Total	$	98,656		(459	)		968,082		(201,734	)
December 31, 2012
Investment securities available for sale:
Obligations of states and political subdivisions	$	166		(1	)		683		(7	)
Mortgage-backed securities:
Government issued or guaranteed		12,107		(65	)		8,804		(164	)
Privately issued residential		121,487		(692	)		773,409		(124,955	)
Privately issued commercial		—		—			919		(26	)
Collateralized debt obligations		—		—			6,043		(1,022	)
Other debt securities		—		—			95,685		(26,900	)
Equity securities		5,535		(1,295	)		2,956		(2,125	)
		139,295		(2,053	)		888,499		(155,199	)
Investment securities held to maturity:
Obligations of states and political subdivisions		1,026		(5	)		3,558		(22	)
Privately issued mortgage-backed securities		—		—			147,273		(94,900	)
		1,026		(5	)		150,831		(94,922	)
Total	$	140,321		(2,058	)		1,039,330		(250,121	)