3. Securities

The amortized cost, gross unrealized gains and losses, and estimated fair value of securities classified as available for sale and held to maturity follow.



Securities Available for Sale
(in thousands)	September 30, 2018								December 31, 2017
			Gross		Gross						Gross		Gross
	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
U.S. Treasury and government agency securities	$	94,366		—		5,054		89,312	$	99,535	$	—	$	2,263	$	97,272
Municipal obligations		243,546		95		10,928		232,713		245,997		1,135		3,346		243,786
Residential mortgage-backed securities		1,793,698		1,969		64,392		1,731,275		1,729,989		5,611		20,387		1,715,213
Commercial mortgage-backed securities		770,245		—		47,363		722,882		704,518		480		17,863		687,135
Collateralized mortgage obligations		143,496		—		4,993		138,503		165,518		4		1,559		163,963
Corporate debt securities		3,500		—		—		3,500		3,500		—		—		3,500
	$	3,048,851	$	2,064	$	132,730	$	2,918,185	$	2,949,057	$	7,230	$	45,418	$	2,910,869



Securities Held to Maturity
(in thousands)	September 30, 2018								December 31, 2017
			Gross		Gross						Gross		Gross
	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
U.S. Treasury and government agency securities	$	50,000		—		708		49,292	$	50,000	$	—	$	289	$	49,711
Municipal obligations		699,470		355		17,809		682,016		723,094		8,323		4,245		727,172
Residential mortgage-backed securities		668,320		—		15,501		652,819		725,748		4,175		2,690		727,233
Commercial mortgage-backed securities		357,428		—		17,429		339,999		317,185		40		3,915		313,310
Collateralized mortgage obligations		1,294,044		—		42,715		1,251,329		1,161,484		572		17,472		1,144,584
	$	3,069,262	$	355	$	94,162	$	2,975,455	$	2,977,511	$	13,110	$	28,611	$	2,962,010

The following tables present the amortized cost and estimated fair value of debt securities available for sale and held to maturity at September 30, 2018 by contractual maturity. Actual maturities will differ from contractual maturities because of rights to call or repay obligations with or without penalties and scheduled and unscheduled principal payments on mortgage-backed securities and collateralized mortgage obligations.



Debt Securities Available for Sale	Amortized		Fair
(in thousands)	Cost		Value
Due in one year or less	$	4,814	$	4,820
Due after one year through five years		54,339		54,077
Due after five years through ten years		1,259,696		1,196,235
Due after ten years		1,730,002		1,663,053
Total available for sale debt securities	$	3,048,851	$	2,918,185

Debt Securities Held to Maturity	Amortized		Fair
(in thousands)	Cost		Value
Due in one year or less	$	24,832	$	24,909
Due after one year through five years		130,348		127,950
Due after five years through ten years		1,452,690		1,407,279
Due after ten years		1,461,392		1,415,317
Total held to maturity securities	$	3,069,262	$	2,975,455

The Company held no securities classified as trading at September 30, 2018 or December 31, 2017.

The fair value and gross unrealized losses for securities classified as available for sale with unrealized losses for the periods indicated follow.



Available for Sale
September 30, 2018	Losses < 12 months				Losses 12 months or >				Total
			Gross				Gross				Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(in thousands)	Value		Losses		Value		Losses		Value		Losses
U.S. Treasury and government agency securities	$	41,765		2,027		47,547		3,027	$	89,312	$	5,054
Municipal obligations		53,337		1,568		165,732		9,360		219,069		10,928
Residential mortgage-backed securities		652,504		11,892		1,029,004		52,500		1,681,508		64,392
Commercial mortgage-backed securities		247,504		8,368		475,379		38,995		722,883		47,363
Collateralized mortgage obligations		82,853		2,836		55,650		2,157		138,503		4,993
	$	1,077,963	$	26,691	$	1,773,312	$	106,039	$	2,851,275	$	132,730



Available for Sale
December 31, 2017	Losses < 12 months				Losses 12 months or >				Total
			Gross				Gross				Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(in thousands)	Value		Losses		Value		Losses		Value		Losses
U.S. Treasury and government agency securities	$	45,616	$	42	$	51,157	$	2,221	$	96,773	$	2,263
Municipal obligations		2,768		11		173,530		3,335		176,298		3,346
Residential mortgage-backed securities		461,835		4,195		898,099		16,192		1,359,934		20,387
Commercial mortgage-backed securities		203,618		995		411,046		16,868		614,664		17,863
Collateralized mortgage obligations		128,174		1,076		35,488		483		163,662		1,559
	$	842,011	$	6,319	$	1,569,320	$	39,099	$	2,411,331	$	45,418

The fair value and gross unrealized losses for securities classified as held to maturity with unrealized losses for the periods indicated follow.



Held to maturity
September 30, 2018	Losses < 12 months				Losses 12 months or >				Total
			Gross				Gross				Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(in thousands)	Value		Losses		Value		Losses		Value		Losses
U.S. Treasury and government agency securities	$	—		—		49,292		708	$	49,292	$	708
Municipal obligations		378,622		7,288		217,955		10,521		596,577		17,809
Residential mortgage-backed securities		454,003		6,996		198,816		8,505		652,819		15,501
Commercial mortgage-backed securities		270,664		11,146		69,335		6,283		339,999		17,429
Collateralized mortgage obligations		572,469		11,263		678,860		31,452		1,251,329		42,715
	$	1,675,758	$	36,693	$	1,214,258	$	57,469	$	2,890,016	$	94,162



Held to maturity
December 31, 2017	Losses < 12 months				Losses 12 months or >				Total
			Gross				Gross				Gross
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
(in thousands)	Value		Losses		Value		Losses		Value		Losses
U.S. Treasury and government agency securities	$	—	$	—	$	49,711	$	289	$	49,711	$	289
Municipal obligations		14,603		19		230,960		4,226		245,563		4,245
Residential mortgage-backed securities		8,815		99		230,277		2,591		239,092		2,690
Commercial mortgage-backed securities		174,882		744		72,499		3,171		247,381		3,915
Collateralized mortgage obligations		570,289		5,653		472,536		11,819		1,042,825		17,472
	$	768,589	$	6,515	$	1,055,983	$	22,096	$	1,824,572		28,611

The unrealized losses relate primarily to changes in market rates on fixed rate debt securities since the respective purchase dates. In all cases, the indicated impairment on these debt securities would be recovered no later than the security’s maturity date or possibly earlier if the market price for the security increases with a reduction in the yield required by the market. None of the unrealized losses relate to the marketability of the securities or the issuers’ abilities to meet contractual obligations. The Company had adequate liquidity as of September 30, 2018 and December 31, 2017 and did not intend to nor believe that it would be required to sell these securities before recovery of the indicated impairment. Accordingly, the unrealized losses on these securities were determined to be temporary. Should the Company’s intent to sell these securities change, the difference between the amortized cost and the fair value will be recognized into earnings at that time.

There were no sales of securities during the nine months ended September 30, 2018. Proceeds from the sales of securities were approximately $213.9 million with no gain or loss for the nine months ended September 30, 2017.

Securities with carrying values totaling $3.1 billion and $3.3 billion at September 30, 2018 and December 31, 2017, respectively, were pledged as collateral, primarily to secure public deposits or securities sold under agreements to repurchase.