Investment Securities, Available-for-Sale (Tables)

12 Months Ended

Dec. 31, 2013

Investments, Debt and Equity Securities [Abstract]

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

	December 31, 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	2.32	%	$	10,405	187	—		10,592
Maturing after five years through ten years	2.00	%	36		—	—		36
	2.32	%	10,441		187	—		10,628
State and local governments
Maturing within one year	2.22	%	5,964		57	—		6,021
Maturing after one year through five years	2.06	%	174,826		3,486	(448	)	177,864
Maturing after five years through ten years	3.21	%	58,835		831	(1,040	)	58,626
Maturing after ten years	4.41	%	1,137,722		27,247	(22,402	)	1,142,567
	4.06	%	1,377,347		31,621	(23,890	)	1,385,078
Corporate bonds
Maturing within one year	2.17	%	91,687		719	—		92,406
Maturing after one year through five years	2.09	%	341,799		3,203	(1,676	)	343,326
Maturing after five years through ten years	2.23	%	6,851		—	(82	)	6,769
	2.11	%	440,337		3,922	(1,758	)	442,501
Residential mortgage-backed securities	2.48	%	1,380,816		14,071	(10,265	)	1,384,622
Total investment securities	3.10	%	$	3,208,941	49,801	(35,913	)	3,222,829

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

	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

	Years ended
(Dollars in thousands)	December 31, 2013			December 31, 2012	December 31, 2011
Gross proceeds	$	181,971		—	18,916
Less amortized cost	(182,270		)	—	(18,570	)
Net (loss) gain on sale of investments	$	(299	)	—	346
Gross gain on sale of investments	$	3,723		—	1,048
Gross loss on sale of investments	(4,022		)	—	(702	)
Net (loss) gain on sale of investments	$	(299	)	—	346

Summary of investments with an unrealized loss position

	December 31, 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
U.S. government sponsored enterprises	$	3	—		—	—		3	—
State and local governments	408,812		(17,838	)	74,161	(6,052	)	482,973	(23,890	)
Corporate bonds	129,515		(1,672	)	1,702	(86	)	131,217	(1,758	)
Residential mortgage-backed securities	457,611		(10,226	)	1,993	(39	)	459,604	(10,265	)
Total temporarily impaired securities	$	995,941	(29,736	)	77,856	(6,177	)	1,073,797	(35,913	)

	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	)