Investment Securities, Available-for-Sale (Tables)

12 Months Ended

Dec. 31, 2012

Investments, Debt and Equity Securities [Abstract]

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

	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

Note 3. Investment Securities, Available-for-Sale (continued)

	December 31, 2011
	Weighted		Amortized		Gross Unrealized			Fair
(Dollars in thousands)	Yield		Cost		Gains	Losses		Value
U.S. government and federal agency
Maturing after one year through five years	1.62	%	$	204	4	—		208
U.S. government sponsored enterprises
Maturing within one year	1.58	%	3,979		17	—		3,996
Maturing after one year through five years	2.36	%	26,399		682	—		27,081
Maturing after five years through ten years	1.90	%	78		—	—		78
	2.26	%	30,456		699	—		31,155
State and local governments
Maturing within one year	1.31	%	4,786		3	(2	)	4,787
Maturing after one year through five years	2.22	%	89,752		2,660	(22	)	92,390
Maturing after five years through ten years	2.59	%	63,143		2,094	(19	)	65,218
Maturing after ten years	4.84	%	845,657		57,138	(535	)	902,260
	4.44	%	1,003,338		61,895	(578	)	1,064,655
Corporate bonds
Maturing after one year through five years	2.55	%	60,810		261	(1,264	)	59,807
Maturing after five years through ten years	2.38	%	2,409		21	—		2,430
	2.54	%	63,219		282	(1,264	)	62,237
Collateralized debt obligations
Maturing after ten years	8.03	%	5,648		—	(282	)	5,366
Residential mortgage-backed securities	1.70	%	1,960,167		10,138	(7,183	)	1,963,122
Total investment securities	2.64	%	$	3,063,032	73,018	(9,307	)	3,126,743

Gain or Loss on sale of Investments

	Years ended
(Dollars in thousands)	December 31, 2012		December 31, 2011		December 31, 2010
Gross proceeds	$	—	18,916		142,925
Less amortized cost	—		(18,570	)	(138,103	)
Net gain on sale of investments	$	—	346		4,822
Gross gain on sale of investments	$	—	1,048		7,779
Gross loss on sale of investments	—		(702	)	(2,957	)
Net gain on sale of investments	$	—	346		4,822

Investments with an unrealized loss position

	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	)

	December 31, 2011
	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	$	26,434	(90	)	9,948	(488	)	36,382	(578	)
Corporate bonds	31,782		(1,264	)	—	—		31,782	(1,264	)
Collateralized debt obligations	—		—		5,366	(282	)	5,366	(282	)
Residential mortgage-backed securities	943,372		(6,850	)	8,244	(333	)	951,616	(7,183	)
Total temporarily impaired securities	$	1,001,588	(8,204	)	23,558	(1,103	)	1,025,146	(9,307	)