Investment Securities

The following table presents the amortized costs, unrealized gains, unrealized losses and approximate fair values of investment securities at December 31, 2015 and 2014:

December 31, 2015



(in thousands)	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
AVAILABLE FOR SALE:
Obligations of states and political subdivisions	$	300,998	$	12,741	$	(622	)	$	313,117
Residential mortgage-backed securities and collateralized mortgage obligations	2,223,742		7,218		(23,540		)	2,207,420
Investments in mutual funds and other equity securities	1,959		43		—			2,002
	$	2,526,699	$	20,002	$	(24,162	)	$	2,522,539
HELD TO MATURITY:
Residential mortgage-backed securities and collateralized mortgage obligations	$	4,609	$	981	$	—		$	5,590
	$	4,609	$	981	$	—		$	5,590

December 31, 2014



(in thousands)	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
AVAILABLE FOR SALE:
U.S. Treasury and agencies	$	213	$	16	$	—		$	229
Obligations of states and political subdivisions	325,189		14,056		(841		)	338,404
Residential mortgage-backed securities and collateralized mortgage obligations	1,951,514		17,398		(11,060		)	1,957,852
Investments in mutual funds and other equity securities	2,016		54		—			2,070
	$	2,278,932	$	31,524	$	(11,901	)	$	2,298,555
HELD TO MATURITY:
Residential mortgage-backed securities and collateralized mortgage obligations	$	5,088	$	358	$	(15	)	$	5,431
Other investment securities	123		—		—			123
	$	5,211	$	358	$	(15	)	$	5,554

Investment securities that were in an unrealized loss position as of December 31, 2015 and December 31, 2014 are presented in the following tables, based on the length of time individual securities have been in an unrealized loss position. In the opinion of management, these securities are considered only temporarily impaired due to changes in market interest rates or the widening of market spreads subsequent to the initial purchase of the securities, and not due to concerns regarding the underlying credit of the issuers or the underlying collateral.

December 31, 2015



(in thousands)	Less than 12 Months				12 Months or Longer				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
	Value		Losses		Value		Losses		Value		Losses
AVAILABLE FOR SALE:
Obligations of states and political subdivisions	$	2,530	$	83	$	8,208	$	539	$	10,738	$	622
Residential mortgage-backed securities and collateralized mortgage obligations	1,256,994		14,465		334,981		9,075		1,591,975		23,540
Total temporarily impaired securities	$	1,259,524	$	14,548	$	343,189	$	9,614	$	1,602,713	$	24,162

December 31, 2014



(in thousands)	Less than 12 Months				12 Months or Longer				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
	Value		Losses		Value		Losses		Value		Losses
AVAILABLE FOR SALE:
Obligations of states and political subdivisions	11,100		547		8,550		294		19,650		841
Residential mortgage-backed securities and collateralized mortgage obligations	220,577		815		495,096		10,245		715,673		11,060
Total temporarily impaired securities	$	231,677	$	1,362	$	503,646	$	10,539	$	735,323	$	11,901
HELD TO MATURITY:
Residential mortgage-backed securities and collateralized mortgage obligations	$	224	$	15	$	—	$	—	$	224	$	15
Total temporarily impaired securities	$	224	$	15	$	—	$	—	$	224	$	15

The unrealized losses on obligations of states and political subdivisions were caused by changes in market interest rates or the widening of market spreads subsequent to the initial purchase of these securities. Management monitors published credit ratings of these securities and no adverse ratings changes have occurred since the date of purchase of obligations of states and political subdivisions which are in an unrealized loss position as of December 31, 2015. Because the decline in fair value is attributable to changes in interest rates or widening market spreads and not credit quality, and because the Bank does not intend to sell the securities in this class and it is not more likely than not that the Bank will be required to sell these securities before recovery of their amortized cost basis, which may include holding each security until maturity, these investments are not considered other-than-temporarily impaired.

All of the available for sale residential mortgage-backed securities and collateralized mortgage obligations portfolio in an unrealized loss position at December 31, 2015 are issued or guaranteed by government sponsored enterprises. The unrealized losses on residential mortgage-backed securities and collateralized mortgage obligations were caused by changes in market interest rates or the widening of market spreads subsequent to the initial purchase of these securities, and not concerns regarding the underlying credit of the issuers or the underlying collateral. It is expected that these securities will not be settled at a price less than the amortized cost of each investment. Because the decline in fair value is attributable to changes in interest rates or widening market spreads and not credit quality, and because the Bank does not intend to sell the securities in this class and it is not more likely than not that the Bank will be required to sell these securities before recovery of their amortized cost basis, which may include holding each security until contractual maturity, these investments are not considered other-than-temporarily impaired.

The following table presents the maturities of investment securities at December 31, 2015:



(in thousands)	Available For Sale				Held To Maturity
	Amortized		Fair		Amortized		Fair
	Cost		Value		Cost		Value
AMOUNTS MATURING IN:
Three months or less	$	4,648	$	4,673	$	—	$	—
Over three months through twelve months	72,886		73,615		6		8
After one year through five years	1,646,982		1,648,510		257		760
After five years through ten years	602,427		595,462		332		808
After ten years	197,797		198,277		4,014		4,014
Other investment securities	1,959		2,002		—		—
	$	2,526,699	$	2,522,539	$	4,609	$	5,590

The amortized cost and fair value of collateralized mortgage obligations and mortgage-backed securities are presented by expected average life, rather than contractual maturity, in the preceding table. Expected maturities may differ from contractual maturities because borrowers have the right to prepay underlying loans without prepayment penalties.

The following table presents the gross realized gains and gross realized losses on the sale of securities available for sale for the years ended December 31, 2015, 2014 and 2013:



(in thousands)	2015				2014				2013
	Gains		Losses		Gains		Losses		Gains		Losses
U.S. Treasury and agencies	$	13	$	—	$	—	$	—	$	—	$	—
Obligations of states and political subdivisions	631		—		3		1		10		1
Residential mortgage-backed securities and collateralized mortgage obligations	3,119		841		2,902		—		—		—
Other debt securities	—		—		—		—		200		—
	$	3,763	$	841	$	2,905	$	1	$	210	$	1

The following table presents, as of December 31, 2015, investment securities which were pledged to secure borrowings, public deposits, and repurchase agreements as permitted or required by law:



(in thousands)	Amortized		Fair
	Cost		Value
To Federal Home Loan Bank to secure borrowings	$	816	$	834
To state and local governments to secure public deposits	1,719,779		1,719,098
Other securities pledged principally to secure repurchase agreements	470,883		467,936
Total pledged securities	$	2,191,478	$	2,187,868