Investment Securities

The following tables present the amortized costs, unrealized gains, unrealized losses and approximate fair values of investment securities at September 30, 2017 and December 31, 2016:



(in thousands)	September 30, 2017
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
AVAILABLE FOR SALE:
U.S. Treasury and agencies	$	40,026	$	—	$	—		$	40,026
Obligations of states and political subdivisions	291,908		6,775		(889		)	297,794
Residential mortgage-backed securities and collateralized mortgage obligations	2,725,745		5,499		(23,689		)	2,707,555
Investments in mutual funds and other equity securities	1,959		24		—			1,983
	$	3,059,638	$	12,298	$	(24,578	)	$	3,047,358
HELD TO MATURITY:
Residential mortgage-backed securities and collateralized mortgage obligations	$	3,905	$	1,114	$	—		$	5,019
	$	3,905	$	1,114	$	—		$	5,019



(in thousands)	December 31, 2016
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
AVAILABLE FOR SALE:
Obligations of states and political subdivisions	$	305,708	$	5,526	$	(3,537	)	$	307,697
Residential mortgage-backed securities and collateralized mortgage obligations	2,428,387		3,664		(40,498		)	2,391,553
Investments in mutual funds and other equity securities	1,959		11		—			1,970
	$	2,736,054	$	9,201	$	(44,035	)	$	2,701,220
HELD TO MATURITY:
Residential mortgage-backed securities and collateralized mortgage obligations	$	4,216	$	1,001	$	—		$	5,217
	$	4,216	$	1,001	$	—		$	5,217

Investment securities that were in an unrealized loss position as of September 30, 2017 and December 31, 2016 are presented in the following tables, based on the length of time individual securities have been in an unrealized loss position.



September 30, 2017
(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	$	13,108	$	147	$	25,256	$	742	$	38,364	$	889
Residential mortgage-backed securities and collateralized mortgage obligations	1,169,351		10,792		667,296		12,897		1,836,647		23,689
Total temporarily impaired securities	$	1,182,459	$	10,939	$	692,552	$	13,639	$	1,875,011	$	24,578



December 31, 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	$	71,571	$	3,065	$	1,828	$	472	$	73,399	$	3,537
Residential mortgage-backed securities and collateralized mortgage obligations	1,855,304		35,981		182,804		4,517		2,038,108		40,498
Total temporarily impaired securities	$	1,926,875	$	39,046	$	184,632	$	4,989	$	2,111,507	$	44,035

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 the published credit ratings of these securities for material rating or outlook changes. As of September 30, 2017, 95% 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 September 30, 2017 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 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.

The following table presents the maturities of investment securities at September 30, 2017:



(in thousands)	Available For Sale				Held To Maturity
	Amortized		Fair		Amortized		Fair
	Cost		Value		Cost		Value
AMOUNTS MATURING IN:
Due within one year	$	1,786	$	1,791	$	—	$	—
Due after one year through five years	101,898		102,915		—		—
Due after five years through ten years	416,627		419,502		18		19
Due after ten years	2,537,368		2,521,167		3,887		5,000
Other investment securities	1,959		1,983		—		—
	$	3,059,638	$	3,047,358	$	3,905	$	5,019

The following tables present the gross realized gains and losses on the sale of securities available for sale for the three and nine months ended September 30, 2017 and 2016:



(in thousands)	Three Months Ended
	September 30, 2017				September 30, 2016
	Gains		Losses		Gains		Losses
Obligations of states and political subdivisions	$	—	$	6	$	—	$	—
	$	—	$	6	$	—	$	—

	Nine Months Ended
	September 30, 2017				September 30, 2016
	Gains		Losses		Gains		Losses
Obligations of states and political subdivisions	$	—	$	9	$	971	$	—
Residential mortgage-backed securities and collateralized mortgage obligations	135		99		270		383
	$	135	$	108	$	1,241	$	383

The following table presents, as of September 30, 2017, 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 the Federal Home Loan Bank to secure borrowings	$	458	$	467
To state and local governments to secure public deposits	926,917		927,182
Other securities pledged principally to secure repurchase agreements	426,540		423,854
Total pledged securities	$	1,353,915	$	1,351,503