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

						Gross		Gross
				Amortized		unrealized		unrealized
September 30, 2014:				cost		gains		losses			Fair value
					($ in Thousands)
Investment securities available for sale:
	U.S. Treasury securities			$	999	$	―	$	(3)	$	996
	Obligations of state and political subdivisions
		(municipal securities)			588,255		26,229		(48)		614,436
	Residential mortgage-related securities:
		Government-sponsored enterprise ("GSE")			3,725,218		59,047		(43,225)		3,741,040
		Private-label			2,475		9		(2)		2,482
	GNMA commercial mortgage-related securities				1,007,068		1,751		(28,217)		980,602
	Other securities (debt and equity)				5,806		60		―		5,866
			Total investment securities available for sale	$	5,329,821	$	87,096	$	(71,495)	$	5,345,422

Investment securities held to maturity:
	Obligations of state and political subdivisions
		(municipal securities)		$	301,941	$	6,875	$	(934)	$	307,882
			Total investment securities held to maturity	$	301,941	$	6,875	$	(934)	$	307,882

						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	$	-	$	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		-		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

(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.

The amortized cost and fair values of investment securities available for sale and held to maturity at September 30, 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		$	28,053	$	28,232		$	-	$	-
Due after one year through five years			224,059		236,326			765		774
Due after five years through ten years			333,788		347,187			105,931		106,998
Due after ten years			9,142		9,480			195,245		200,110
	Total debt securities		595,042		621,225			301,941		307,882
Residential mortgage-related securities:
	GSE		3,725,218		3,741,040			-		-
	Private-label		2,475		2,482			-		-
GNMA commercial mortgage-related securities			1,007,068		980,602			-		-
Equity securities			18		73			-		-
	Total investment securities	$	5,329,821	$	5,345,422		$	301,941	$	307,882

Ratio of Fair Value to Amortized Cost					100.3	%				102.0	%

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 September 30, 2014.

			Less than 12 months					12 months or more						Total
			Number of	Unrealized			Fair	Number of	Unrealized			Fair	Unrealized			Fair
September 30, 2014:			Securities		Losses		Value	Securities		Losses		Value		Losses		Value
					($ in Thousands)
Investment securities available for sale:
	U.S. Treasury securities		1	$	(3)	$	996	0	$	―	$	―	$	(3)	$	996
	Obligations of state and political
		subdivisions (municipal securities)	5		(1)	$	1,799	13		(47)	$	5,647		(48)	$	7,446
	Residential mortgage-related securities:
		GSE	30		(1,472)		331,085	64		(41,753)		1,389,945		(43,225)		1,721,030
		Private-label	1		(1)		1,889	2		(1)		30		(2)		1,919
	GNMA commercial mortgage-related securities		12		(1,927)		363,315	15		(26,290)		390,443		(28,217)		753,758
		Total		$	(3,404)	$	699,084		$	(68,091)	$	1,786,065	$	(71,495)	$	2,485,149
Investment securities held to maturity:
	Obligations of state and political
		subdivisions (municipal securities)	39	$	(55)	$	14,443	119	$	(879)	$	55,522	$	(934)	$	69,965
		Total		$	(55)	$	14,443		$	(879)	$	55,522	$	(934)	$	69,965

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	1		(3,988)		45,950		(27,842)		489,412
	Other debt securities		5		(43)		6,452	0		-		-		(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

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.

Based on the Corporation's evaluation, management does not believe any unrealized loss at September 30, 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 Government National Mortgage Association ("GNMA"), 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 securities issued by GNMA. The unrealized losses reported for municipal securities relate to various state and local political subdivisions and school districts. 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 improvement in the unrealized loss position of the investment securities portfolio was due to a reduction in the overall level of interest rates from December 31, 2013 to September 30, 2014, as well as spread compression on mortgage-related and municipal securities, which increased the fair value of investment securities.

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 nine months ended September 30, 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 or abandoned			―		6,279		6,279
Balance of credit-related other-than-temporary							.
	impairment at September 30, 2014	$	―	$	―	$	―

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 $118 million at September 30, 2014 and $110 million at December 31, 2013 and Federal Reserve Bank stock of $71 million at both September 30, 2014 and December 31, 2013.