3. Securities

The amortized cost and estimated fair value of securities classified as available for sale and held to maturity follow.



Securities Available for Sale
(in thousands)	March 31, 2017								December 31, 2016
			Gross		Gross						Gross		Gross
	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
US Treasury and government agency securities	$	76,049	$	—	$	1,553	$	74,496	$	56,751	$	—	$	1,923	$	54,828
Municipal obligations		251,416		157		10,537		241,036		253,228		113		11,186		242,155
Residential mortgage-backed securities		1,568,001		10,377		18,961		1,559,417		1,620,191		10,592		19,428		1,611,355
Commercial mortgage-backed securities		450,197		211		22,360		428,048		425,750		—		23,159		402,591
Collateralized mortgage obligations		192,372		491		599		192,264		202,580		490		591		202,479
Corporate debt securities		3,500		—		—		3,500		3,500		—		—		3,500
	$	2,541,535	$	11,236	$	54,010	$	2,498,761	$	2,562,000	$	11,195	$	56,287	$	2,516,908



Securities Held to Maturity
(in thousands)	March 31, 2017								December 31, 2016
			Gross		Gross						Gross		Gross
	Amortized		Unrealized		Unrealized		Fair		Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value		Cost		Gains		Losses		Value
US Treasury and government agency securities	$	50,000	$	—	$	55	$	49,945	$	50,000	$	—	$	44	$	49,956
Municipal obligations		734,075		3,345		17,604		719,816		648,093		2,147		20,175		630,065
Residential mortgage-backed securities		830,522		3,481		1,980		832,023		862,162		4,329		3,068		863,423
Commercial mortgage-backed securities		75,722		—		4,348		71,374		75,739		—		4,038		71,701
Collateralized mortgage obligations		812,193		1,588		9,519		804,262		864,226		1,420		10,674		854,972
	$	2,502,512	$	8,414	$	33,506	$	2,477,420	$	2,500,220	$	7,896	$	37,999	$	2,470,117

The following table presents the amortized cost and estimated fair value of debt securities at March 31, 2017 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.



(in thousands)	Amortized		Fair
Debt Securities Available for Sale	Cost		Value
Due in one year or less	$	4,711	$	4,735
Due after one year through five years		40,658		41,205
Due after five years through ten years		1,025,204		999,011
Due after ten years		1,470,962		1,453,810
Total available for sale debt securities	$	2,541,535	$	2,498,761

	Amortized		Fair
Debt Securities Held to Maturity	Cost		Value
Due in one year or less	$	10,520	$	10,624
Due after one year through five years		124,250		125,558
Due after five years through ten years		838,244		817,979
Due after ten years		1,529,498		1,523,259
Total held to maturity securities	$	2,502,512	$	2,477,420

The Company held no securities classified as trading at March 31, 2017 or December 31, 2016.

The details for securities classified as available for sale with unrealized losses for the periods indicated follow.



Available for Sale
March 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
US Treasury and government agency securities	$	74,460		1,553	$	—	$	—	$	74,460	$	1,553
Municipal obligations		228,433		10,537		—		—		228,433		10,537
Residential mortgage-backed securities		1,051,706		18,885		3,110		76		1,054,816		18,961
Commercial mortgage-backed securities		403,123		22,360		—		—		403,123		22,360
Collateralized mortgage obligations		78,217		599		—		—		78,217		599
	$	1,835,939	$	53,934	$	3,110	$	76	$	1,839,049	$	54,010



Available for Sale
December 31, 2016	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
US Treasury and government agency securities	$	54,788	$	1,923	$	—	$	—	$	54,788	$	1,923
Municipal obligations		228,588		11,186		—		—		228,588		11,186
Residential mortgage-backed securities		1,087,644		19,359		3,738		69		1,091,382		19,428
Commercial mortgage-backed securities		402,591		23,159		—		—		402,591		23,159
Collateralized mortgage obligations		83,701		591		—		—		83,701		591
	$	1,857,312	$	56,218	$	3,738	$	69	$	1,861,050	$	56,287

The details for securities classified as held to maturity with unrealized losses for the periods indicated follow.



Held to maturity
March 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
US Treasury and government agency securities	$	49,946	$	55	$	—	$	—	$	49,946	$	55
Municipal obligations		454,266		17,331		7,269		273		461,535		17,604
Residential mortgage-backed securities		279,443		1,980		—		—		279,443		1,980
Commercial mortgage-backed securities		71,373		4,348		—		—		71,373		4,348
Collateralized mortgage obligations		506,593		6,343		104,011		3,176		610,604		9,519
	$	1,361,621	$	30,057	$	111,280	$	3,449	$	1,472,901	$	33,506



Held to maturity
December 31, 2016	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	$	49,956	$	44	$	—	$	—	$	49,956	$	44
Municipal obligations		494,470		19,706		11,750		469		506,220		20,175
Residential mortgage-backed securities		278,369		3,068		—		—		278,369		3,068
Commercial mortgage-backed securities		71,701		4,038		—		—		71,701		4,038
Collateralized mortgage obligations		618,739		7,296		115,375		3,378		734,114		10,674
	$	1,513,235	$	34,152	$	127,125	$	3,847	$	1,640,360	$	37,999

The unrealized losses primarily relate 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 issuer’s ability to meet contractual obligations. The Company believes it has adequate liquidity and, therefore, does not plan to and, more likely than not, will not be required to sell these securities before recovery of the indicated impairment. Accordingly, the unrealized losses on these securities have been determined to be temporary.

There were no sales of securities for the three months ended March 31, 2017. Proceeds from the sales of securities were approximately $47.8 million with a gross gain of $0.3 million for the three months ended March 31, 2016, respectively.

Securities with carrying values totaling $4.0 billion at March 31, 2017 and $3.8 billion at December 31, 2016 were pledged as collateral primarily to secure public deposits or securities sold under agreements to repurchase.