Investment Securities

The following table presents the amortized costs, unrealized gains, unrealized losses and approximate fair values of investment securities at June 30, 2016 and December 31, 2015:



(in thousands)	June 30, 2016
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
AVAILABLE FOR SALE:
Obligations of states and political subdivisions	$	284,421	$	13,956	$	(271	)	$	298,106
Residential mortgage-backed securities and collateralized mortgage obligations	2,158,709		25,233		(2,019		)	2,181,923
Investments in mutual funds and other equity securities	1,959		84		—			2,043
	$	2,445,089	$	39,273	$	(2,290	)	$	2,482,072
HELD TO MATURITY:
Residential mortgage-backed securities and collateralized mortgage obligations	$	4,382	$	868	$	—		$	5,250
	$	4,382	$	868	$	—		$	5,250



(in thousands)	December 31, 2015
	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

Investment securities that were in an unrealized loss position as of June 30, 2016 and December 31, 2015 are presented in the following tables, based on the length of time individual securities have been in an unrealized loss position.



June 30, 2016
(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	$	—	$	—	$	2,029	$	271	$	2,029	$	271
Residential mortgage-backed securities and collateralized mortgage obligations	9,803		28		241,289		1,991		251,092		2,019
Total temporarily impaired securities	$	9,803	$	28	$	243,318	$	2,262	$	253,121	$	2,290



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

The unrealized losses on obligations of 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 the published credit ratings of these securities for material rating or outlook changes. As of June 30, 2016, 92% of these securities were rated A3/A- or higher by rating agencies. Substantially all of the Company's obligations of states and political subdivisions are general obligation issuances. All of the available for sale residential mortgage-backed securities and collateralized mortgage obligations portfolio in an unrealized loss position at June 30, 2016 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 be settled at a price at least equal to 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 and it is not likely 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 June 30, 2016:



(in thousands)	Available For Sale				Held To Maturity
	Amortized		Fair		Amortized		Fair
	Cost		Value		Cost		Value
AMOUNTS MATURING IN:
Three months or less	$	4,655	$	4,665	$	—	$	—
Over three months through twelve months	101,270		102,536		4		4
After one year through five years	1,607,293		1,630,492		188		496
After five years through ten years	531,111		540,023		367		857
After ten years	198,801		202,313		3,823		3,893
Other investment securities	1,959		2,043		—		—
	$	2,445,089	$	2,482,072	$	4,382	$	5,250

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 losses on the sale of securities available for sale for the three and six months ended June 30, 2016 and 2015:



(in thousands)	Three Months Ended
	June 30, 2016				June 30, 2015
	Gains		Losses		Gains		Losses
Obligations of states and political subdivisions	$	275	$	—	$	—	$	—
Residential mortgage-backed securities and collateralized mortgage obligations	270		383		226		207
	$	545	$	383	$	226	$	207

	Six Months Ended
	June 30, 2016				June 30, 2015
	Gains		Losses		Gains		Losses
Obligations of states and political subdivisions	$	971	$	—	$	—	$	—
Residential mortgage-backed securities and collateralized mortgage obligations	270		383		542		407
	$	1,241	$	383	$	542	$	407

The following table presents, as of June 30, 2016, 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	$	699	$	723
To state and local governments to secure public deposits	1,563,608		1,589,716
Other securities pledged principally to secure repurchase agreements	570,194		576,532
Total pledged securities	$	2,134,501	$	2,166,971