Investment Securities, Available-for-Sale (Tables)

9 Months Ended

Sep. 30, 2013

Investments, Debt and Equity Securities [Abstract]

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

	September 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	2.29	%	$	11,278	240	—		11,518
Maturing after five years through ten years	1.82	%	38		—	—		38
	2.29	%	11,316		240	—		11,556
State and local governments
Maturing within one year	2.18	%	6,059		52	—		6,111
Maturing after one year through five years	2.10	%	162,569		3,096	(431	)	165,234
Maturing after five years through ten years	3.17	%	57,892		1,122	(832	)	58,182
Maturing after ten years	4.46	%	1,104,890		28,571	(21,604	)	1,111,857
	4.10	%	1,331,410		32,841	(22,867	)	1,341,384
Corporate bonds
Maturing within one year	2.10	%	73,064		736	—		73,800
Maturing after one year through five years	2.10	%	358,034		2,890	(2,852	)	358,072
Maturing after five years through ten years	2.22	%	11,058		—	(85	)	10,973
	2.10	%	442,156		3,626	(2,937	)	442,845
Residential mortgage-backed securities	2.44	%	1,515,728		15,357	(7,917	)	1,523,168
Total investment securities	3.06	%	$	3,300,610	52,064	(33,721	)	3,318,953

	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				Nine Months ended
(Dollars in thousands)	September 30, 2013			September 30, 2012	September 30, 2013		September 30, 2012
Gross proceeds	$	102,483		—	181,971		—
Less amortized cost	(102,886		)	—	(182,270	)	—
Net loss on sale of investments	$	(403	)	—	(299	)	—
Gross gain on sale of investments	$	3,467		—	3,723		—
Gross loss on sale of investments	(3,870		)	—	(4,022	)	—
Net loss on sale of investments	$	(403	)	—	(299	)	—

Summary of investments with an unrealized loss position

	September 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	$	405,834	(21,121	)	22,373	(1,746	)	428,207	(22,867	)
Corporate bonds	189,130		(2,937	)	—	—		189,130	(2,937	)
Residential mortgage-backed securities	446,642		(7,917	)	—	—		446,642	(7,917	)
Total temporarily impaired securities	$	1,041,606	(31,975	)	22,373	(1,746	)	1,063,979	(33,721	)

	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	)