Investment Securities

The following tables present the amortized costs, unrealized gains, unrealized losses and approximate fair values of investment securities at March 31, 2019 and December 31, 2018:



(in thousands)	March 31, 2019
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
AVAILABLE FOR SALE:
U.S. Treasury and agencies	$	19,998	$	—	$	(209	)	$	19,789
Obligations of states and political subdivisions	300,704		5,630		(671		)	305,663
Residential mortgage-backed securities and collateralized mortgage obligations	2,609,586		7,082		(47,342		)	2,569,326
	$	2,930,288	$	12,712	$	(48,222	)	$	2,894,778
HELD TO MATURITY:
Residential mortgage-backed securities and collateralized mortgage obligations	$	3,478	$	1,039	$	—		$	4,517
	$	3,478	$	1,039	$	—		$	4,517



(in thousands)	December 31, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
AVAILABLE FOR SALE:
U.S. Treasury and agencies	$	40,002	$	—	$	(346	)	$	39,656
Obligations of states and political subdivisions	308,972		2,785		(2,586		)	309,171
Residential mortgage-backed securities and collateralized mortgage obligations	2,696,913		3,590		(72,222		)	2,628,281
	$	3,045,887	$	6,375	$	(75,154	)	$	2,977,108
HELD TO MATURITY:
Residential mortgage-backed securities and collateralized mortgage obligations	$	3,606	$	1,038	$	—		$	4,644
	$	3,606	$	1,038	$	—		$	4,644

Investment securities that were in an unrealized loss position as of March 31, 2019 and December 31, 2018 are presented in the following tables, based on the length of time individual securities have been in an unrealized loss position.



(in thousands)	March 31, 2019
	Less than 12 Months				12 Months or Longer				Total
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
AVAILABLE FOR SALE:
U.S. Treasury and agencies	$	—	$	—	$	19,789	$	209	$	19,789	$	209
Obligations of states and political subdivisions	—		—		35,434		671		35,434		671
Residential mortgage-backed securities and collateralized mortgage obligations	90,992		1,148		2,090,133		46,194		2,181,125		47,342
Total temporarily impaired securities	$	90,992	$	1,148	$	2,145,356	$	47,074	$	2,236,348	$	48,222



(in thousands)	December 31, 2018
	Less than 12 Months				12 Months or Longer				Total
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
AVAILABLE FOR SALE:
U.S. Treasury and agencies	$	—	$	—	$	39,656	$	346	$	39,656	$	346
Obligations of states and political subdivisions	59,963		800		38,691		1,786		98,654		2,586
Residential mortgage-backed securities and collateralized mortgage obligations	332,103		5,432		1,992,546		66,790		2,324,649		72,222
Total temporarily impaired securities	$	392,066	$	6,232	$	2,070,893	$	68,922	$	2,462,959	$	75,154

The unrealized losses on U.S. treasury and agencies securities are due to increases in market interest rates and not due to the underlying credit of the issuers. 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. 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 March 31, 2019 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 unrealized loss 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 contractual maturities of investment securities at March 31, 2019:



(in thousands)	Available For Sale				Held To Maturity
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due within one year	$	1,414	$	1,426	$	—	$	—
Due after one year through five years	93,154		93,223		—		—
Due after five years through ten years	377,171		375,130		14		14
Due after ten years	2,458,549		2,424,999		3,464		4,503
	$	2,930,288	$	2,894,778	$	3,478	$	4,517

The following table presents, as of March 31, 2019, investment securities which were pledged to secure borrowings, public deposits, and repurchase agreements as permitted or required by law:



(in thousands)	Amortized Cost		Fair Value
To state and local governments to secure public deposits	$	898,047	$	888,094
Other securities pledged principally to secure repurchase agreements	430,034		422,461
Total pledged securities	$	1,328,081	$	1,310,555