Investment Securities, Available-for-Sale (Tables)

9 Months Ended

Sep. 30, 2012

Investments, Debt and Equity Securities [Abstract]

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

	September 30, 2012
	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	%	$	202	2	—		204
U.S. government sponsored enterprises
Maturing after one year through five years	2.32	%	19,376		413	—		19,789
Maturing after five years through ten years	1.90	%	70		1	—		71
	2.32	%	19,446		414	—		19,860
State and local governments
Maturing within one year	0.95	%	45,469		8	(3	)	45,474
Maturing after one year through five years	2.11	%	143,651		4,652	(109	)	148,194
Maturing after five years through ten years	2.83	%	43,065		1,406	(50	)	44,421
Maturing after ten years	4.71	%	918,714		81,821	(746	)	999,789
	4.16	%	1,150,899		87,887	(908	)	1,237,878
Corporate bonds
Maturing within one year	1.63	%	21,420		108	—		21,528
Maturing after one year through five years	2.35	%	200,106		3,355	(28	)	203,433
Maturing after five years through ten years	2.30	%	18,088		437	(7	)	18,518
	2.28	%	239,614		3,900	(35	)	243,479
Collateralized debt obligations
Maturing after ten years	8.03	%	2,847		—	(85	)	2,762
Residential mortgage-backed securities	1.87	%	2,077,671		10,489	(5,988	)	2,082,172
Total investment securities	2.66	%	$	3,490,679	102,692	(7,016	)	3,586,355

	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

	Three Months ended				Nine Months ended
(Dollars in thousands)	September 30, 2012		September 30, 2011		September 30, 2012	September 30, 2011
Gross proceeds	$	—	10,708		—	18,916
Less amortized cost	—		(9,895	)	—	(18,570	)
Net gain on sale of investments	$	—	813		—	346
Gross gain on sale of investments	$	—	825		—	1,048
Gross loss on sale of investments	—		(12	)	—	(702	)
Net gain on sale of investments	$	—	813		—	346

Summary of investments with an unrealized loss position

	September 30, 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	$	98,691	(823	)	5,418	(85	)	104,109	(908	)
Corporate bonds	13,024		(35	)	—	—		13,024	(35	)
Collateralized debt obligations	—		—		2,762	(85	)	2,762	(85	)
Residential mortgage-backed securities	844,499		(4,396	)	118,764	(1,592	)	963,263	(5,988	)
Total temporarily impaired securities	$	956,214	(5,254	)	126,944	(1,762	)	1,083,158	(7,016	)

	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	)