Investment Securities, Available-for-Sale (Tables)

6 Months Ended

Jun. 30, 2013

Investments, Debt and Equity Securities [Abstract]

Comparison of amortized cost and estimated fair value of investment securities designated as available-for-sale

	June 30, 2013
	Weighted		Amortized		Gross Unrealized			Fair
(Dollars in thousands)	Yield		Cost		Gains	Losses		Value
U.S. government sponsored enterprises
Maturing after one year through five years	2.27	%	$	12,840	270	—		13,110
Maturing after five years through ten years	1.71	%	40		1	—		41
	2.27	%	12,880		271	—		13,151
State and local governments
Maturing within one year	2.02	%	5,066		41	—		5,107
Maturing after one year through five years	2.07	%	158,331		3,063	(265	)	161,129
Maturing after five years through ten years	3.11	%	55,026		904	(656	)	55,274
Maturing after ten years	4.53	%	1,089,519		44,313	(15,466	)	1,118,366
	4.17	%	1,307,942		48,321	(16,387	)	1,339,876
Corporate bonds
Maturing within one year	2.06	%	64,391		630	—		65,021
Maturing after one year through five years	2.10	%	357,036		2,571	(3,173	)	356,434
Maturing after five years through ten years	2.27	%	21,635		53	(346	)	21,342
	2.10	%	443,062		3,254	(3,519	)	442,797
Residential mortgage-backed securities	2.18	%	1,917,954		13,728	(6,129	)	1,925,553
Total investment securities	2.88	%	$	3,681,838	65,574	(26,035	)	3,721,377

	December 31, 2012
	Weighted		Amortized		Gross Unrealized			Fair
(Dollars in thousands)	Yield		Cost		Gains	Losses		Value
U.S. government and federal agency
Maturing within one year	1.62	%	$	201	1	—		202
U.S. government sponsored enterprises
Maturing after one year through five years	2.30	%	17,064		371	—		17,435
Maturing after five years through ten years	2.03	%	44		1	—		45
	2.29	%	17,108		372	—		17,480
State and local governments
Maturing within one year	2.01	%	4,288		28	(2	)	4,314
Maturing after one year through five years	2.11	%	149,497		4,142	(142	)	153,497
Maturing after five years through ten years	2.95	%	38,346		1,102	(99	)	39,349
Maturing after ten years	4.70	%	935,897		82,823	(1,362	)	1,017,358
	4.29	%	1,128,028		88,095	(1,605	)	1,214,518
Corporate bonds
Maturing within one year	1.73	%	18,412		51	—		18,463
Maturing after one year through five years	2.22	%	250,027		4,018	(238	)	253,807
Maturing after five years through ten years	2.23	%	16,144		381	—		16,525
	2.19	%	284,583		4,450	(238	)	288,795
Collateralized debt obligations
Maturing after ten years	8.03	%	1,708		—	—		1,708
Residential mortgage-backed securities	1.95	%	2,156,049		8,860	(4,607	)	2,160,302
Total investment securities	2.71	%	$	3,587,677	101,778	(6,450	)	3,683,005

Gain or loss on sale of Investments

	Three Months ended				Six Months ended
(Dollars in thousands)	June 30, 2013			June 30, 2012	June 30, 2013			June 30, 2012
Gross proceeds	$	75,649		—	$	79,488		—
Less amortized cost	(75,408		)	—	(79,384		)	—
Net gain on sale of investments	$	241		—	$	104		—
Gross gain on sale of investments	$	256		—	$	256		—
Gross loss on sale of investments	(15		)	—	(152		)	—
Net gain on sale of investments	$	241		—	$	104		—

Summary of investments with an unrealized loss position

	June 30, 2013
	Less than 12 Months				12 Months or More			Total
(Dollars in thousands)	Fair Value		Unrealized Loss		Fair Value	Unrealized Loss		Fair Value	Unrealized Loss
State and local governments	$	312,576	(15,987	)	10,434	(400	)	323,010	(16,387	)
Corporate bonds	211,592		(3,519	)	—	—		211,592	(3,519	)
Residential mortgage-backed securities	511,542		(6,086	)	15,991	(43	)	527,533	(6,129	)
Total temporarily impaired securities	$	1,035,710	(25,592	)	26,425	(443	)	1,062,135	(26,035	)

	December 31, 2012
	Less than 12 Months				12 Months or More			Total
(Dollars in thousands)	Fair Value		Unrealized Loss		Fair Value	Unrealized Loss		Fair Value	Unrealized Loss
State and local governments	$	102,896	(1,531	)	4,533	(74	)	107,429	(1,605	)
Corporate bonds	41,856		(238	)	—	—		41,856	(238	)
Residential mortgage-backed securities	955,235		(4,041	)	62,905	(566	)	1,018,140	(4,607	)
Total temporarily impaired securities	$	1,099,987	(5,810	)	67,438	(640	)	1,167,425	(6,450	)