The amortized cost and fair values of investment securities available for sale and held to maturity were as follows.

						Gross		Gross
				Amortized		unrealized		unrealized
March 31, 2014:				cost		gains		losses			Fair value
					($ in Thousands)
Investment securities available for sale:
	U.S. Treasury securities			$	1,001	$	1	$	0	$	1,002
	Obligations of state and political subdivisions
		(municipal securities)			640,433		25,539		(628)		665,344
	Residential mortgage-related securities:
		Government-sponsored enterprise ("GSE")			3,767,991		60,240		(58,989)		3,769,242
		Private-label			2,699		16		(18)		2,697
	GNMA commercial mortgage-related securities				839,488		1,703		(27,624)		813,567
	Asset-backed securities (1)				21,318		―		(36)		21,282
	Other securities (debt and equity)				4,720		62		(8)		4,774
			Total investment securities available for sale	$	5,277,650	$	87,561	$	(87,303)	$	5,277,908

Investment securities held to maturity:
	Obligations of state and political subdivisions
		(municipal securities)		$	193,759	$	2,372	$	(2,985)	$	193,146
			Total investment securities held to maturity	$	193,759	$	2,372	$	(2,985)	$	193,146

(1) The asset-backed securities position is largely comprised of senior, floating rate, tranches of student loan securities issued by SLM Corp and guaranteed under the Federal Family Education Loan Program.

						Gross		Gross
				Amortized		unrealized		unrealized
December 31, 2013:				cost		gains		losses			Fair value
					($ in Thousands)
Investment securities available for sale:
	U.S. Treasury securities			$	1,001	$	1	$	0	$	1,002
	Obligations of state and political subdivisions
		(municipal securities)			653,758		23,855		(1,533)		676,080
	Residential mortgage-related securities:
		GSE			3,855,467		61,542		(78,579)		3,838,430
		Private-label			3,035		16		(37)		3,014
	GNMA commercial mortgage-related securities				673,555		1,764		(27,842)		647,477
	Asset-backed securities (1)				23,049		10		0		23,059
	Other securities (debt and equity)				60,711		855		(43)		61,523
			Total investment securities available for sale	$	5,270,576	$	88,043	$	(108,034)	$	5,250,585

Investment securities held to maturity:
	Obligations of state and political subdivisions
		(municipal securities)		$	175,210	$	401	$	(5,722)	$	169,889
			Total investment securities held to maturity	$	175,210	$	401	$	(5,722)	$	169,889

The amortized cost and fair values of investment securities available for sale and held to maturity at March 31, 2014, are shown below. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.

		Available for Sale					Held to Maturity
($ in Thousands)		Amortized Cost			Fair Value		Amortized Cost			Fair Value
Due in one year or less		$	23,534	$	23,714		$	-	$	-
Due after one year through five years			202,811		212,978			230		231
Due after five years through ten years			404,168		418,321			82,187		81,033
Due after ten years			15,623		16,054			111,342		111,882
	Total debt securities		646,136		671,067			193,759		193,146
Residential mortgage-related securities:
	GSE		3,767,991		3,769,242			-		-
	Private label		2,699		2,697			-		-
GNMA commercial mortgage-related securities			839,488		813,567			-		-
Asset-backed securities			21,318		21,282			-		-
Equity securities			18		53			-		-
	Total investment securities	$	5,277,650	$	5,277,908		$	193,759	$	193,146

Ratio of Fair Value to Amortized Cost					100.00	%				99.7	%

The following represents gross unrealized losses and the related fair value of investment securities available for sale and held to maturity, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at March 31, 2014.

			Less than 12 months					12 months or more						Total
			Number of	Unrealized			Fair	Number of	Unrealized			Fair	Unrealized			Fair
March 31, 2014:			Securities		Losses		Value	Securities		Losses		Value		Losses		Value
					($ in Thousands)
Investment securities available for sale:
	Obligations of state and political
		subdivisions (municipal securities)	86	$	(620)	$	36,357	1	$	(8)	$	271	$	(628)	$	36,628
	Residential mortgage-related securities:
		GSE	86		(36,552)		1,439,729	19		(22,437)		555,664		(58,989)		1,995,393
		Private-label	1		(17)		1,917	2		(1)		38		(18)		1,955
	GNMA commercial mortgage-related securities		17		(12,541)		425,310	7		(15,083)		209,336		(27,624)		634,646
	Asset backed securities		2		(36)		21,282	0		―		―		(36)		21,282
	Other debt securities		3		(8)		1,492	0		―		―		(8)		1,492
		Total		$	(49,774)	$	1,926,087		$	(37,529)	$	765,309	$	(87,303)	$	2,691,396
Investment securities held to maturity:
	Obligations of state and political
		subdivisions (municipal securities)	168	$	(2,377)	$	76,708	25	$	(608)	$	11,272	$	(2,985)	$	87,980
		Total		$	(2,377)	$	76,708		$	(608)	$	11,272	$	(2,985)	$	87,980

The Corporation reviews the investment securities portfolio on a quarterly basis to monitor its exposure to other-than-temporary impairment. A determination as to whether a security's decline in fair value is other-than-temporary takes into consideration numerous factors and the relative significance of any single factor can vary by security. Some factors the Corporation may consider in the other-than-temporary impairment analysis include, the length of time and extent to which the security has been in an unrealized loss position, changes in security ratings, financial condition and near-term prospects of the issuer, as well as security and industry specific economic conditions. In addition, with regards to its debt securities, the Corporation may also evaluate payment structure, whether there are defaulted payments or expected defaults, prepayment speeds, and the value of any underlying collateral. For certain debt securities in unrealized loss positions, the Corporation prepares cash flow analyses to compare the present value of cash flows expected to be collected from the security with the amortized cost basis of the security.

Based on the Corporation's evaluation, management does not believe any unrealized loss at March 31, 2014 represents an other-than-temporary impairment as these unrealized losses are primarily attributable to changes in interest rates and the current market conditions, and not credit deterioration. The unrealized losses reported for residential mortgage-related securities relate to private-label residential mortgage-related securities as well as residential mortgage-related securities issued by government-sponsored enterprises such as the Federal National Mortgage Association (“FNMA”) and the Federal Home Loan Mortgage Corporation (“FHLMC”). The unrealized losses reported for commercial mortgage-related securities relate to government agency issued securities, Government National Mortgage Association ("GNMA"). The Corporation currently does not intend to sell nor does it believe that it will be required to sell the securities contained in the above unrealized losses table before recovery of their amortized cost basis.

The following is a summary of the credit loss portion of other-than-temporary impairment recognized in earnings on debt securities for the year ended December 31, 2013 and the three months ended March 31, 2014, respectively.

		Private-label
		Mortgage-Related		Trust Preferred
		Securities		Debt Securities			Total
		($ in Thousands)
Balance of credit-related other-than-temporary
	impairment at December 31, 2012	$	(532)	$	(6,336)	$	(6,868)
Reduction due to credit impaired securities sold			532		57		589
Balance of credit-related other-than-temporary							.
	impairment at December 31, 2013	$	―	$	(6,279)	$	(6,279)
Reduction due to credit impaired securities sold			―		765		765
Balance of credit-related other-than-temporary							.
	impairment at March 31, 2014	$	―	$	(5,514)	$	(5,514)

For comparative purposes, the following represents gross unrealized losses and the related fair value of investment securities available for sale and held to maturity, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position, at December 31, 2013.

					Less than 12 months					12 months or more				Total
			Number					Number
			of	Unrealized				of	Unrealized				Unrealized
December 31, 2013:			Securities	Losses		Fair Value		Securities	Losses		Fair Value		Losses		Fair Value
					($ in Thousands)
Investment securities available for sale:
	Obligations of state and political
		subdivisions (municipal securities)	113	$	(1,525)	$	47,044	1	$	(8)	$	273	$	(1,533)	$	47,317
	Residential mortgage-related securities:
		GSE	106		(57,393)		1,887,784	15		(21,186)		421,082		(78,579)		2,308,866
		Private label	2		(37)		2,105	1		-		35		(37)		2,140
	GNMA commercial mortgage-related securities		19		(23,854)		443,462	0		(3,988)		45,950		(27,842)		489,412
	Other debt securities		5		(43)		6,452	1		-		-		(43)		6,452
		Total		$	(82,852)	$	2,386,847		$	(25,182)	$	467,340	$	(108,034)	$	2,854,187

Investment securities held to maturity:
	Obligations of state and political
		subdivisions (municipal securities)	298	$	(5,339)	$	124,435	10	$	(383)	$	5,010	$	(5,722)	$	129,445
		Total		$	(5,339)	$	124,435		$	(383)	$	5,010	$	(5,722)	$	129,445

Federal Home Loan Bank (“FHLB”) and Federal Reserve Bank Stocks: The Corporation is required to maintain Federal Reserve stock and FHLB stock as a member of both the Federal Reserve System and the FHLB, and in amounts as required by these institutions. These equity securities are “restricted” in that they can only be sold back to the respective institutions or another member institution at par. Therefore, they are less liquid than other marketable equity securities and their fair value is equal to amortized cost. The Corporation had FHLB stock of $110 million at both March 31, 2014 and December 31, 2013 and Federal Reserve Bank stock of $71 million at both March 31, 2014 and December 31, 2013.

The Corporation reviewed these securities for impairment, including but not limited to, consideration of operating performance, the severity and duration of market value declines, as well as its liquidity and funding position. After evaluating all of these considerations, the Corporation believes the cost of these investments will be recovered and no impairment has been recorded on these securities during 2013 or the first three months of 2014.