2.	INTEREST-BEARING TIME DEPOSITS IN BANKS AND SECURITIES:

Interest-bearing time deposits in banks totaled $1,707,000 and $3,495,000 at December 31, 2016 and 2015, respectively, and have original maturities generally ranging from one to three years.

A summary of the Company’s available-for-sale securities as of December 31, 2016 and 2015 are as follows (in thousands):


	December 31, 2016
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
Securities available-for-sale:

U.S. Treasury securities	$	10,649	$	19	$	—		$	10,668
Obligations of U.S. government sponsored enterprises and agencies		113,450		253		—			113,703
Obligations of state and political subdivisions		1,534,095		40,194		(10,013	)		1,564,276
Corporate bonds and other		51,920		476		(3	)		52,393
Residential mortgage-backed securities		848,614		8,260		(5,513	)		851,361
Commercial mortgage-backed securities		269,044		622		(1,230	)		268,436


Total securities available-for-sale	$	2,827,772	$	49,824	$	(16,759	)	$	2,860,837


	December 31, 2015
	Amortized Cost Basis		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Estimated Fair Value
Securities available-for-sale:

U.S. Treasury securities	$	10,792	$	5	$	(2	)	$	10,795
Obligations of U.S. government sponsored enterprises and agencies		148,393		268		(107	)		148,554
Obligations of state and political subdivisions		1,379,879		71,382		(134	)		1,451,127
Corporate bonds and other		86,182		1,778		(5	)		87,955
Residential mortgage-backed securities		781,648		10,993		(3,759	)		788,882
Commercial mortgage-backed securities		247,991		429		(1,834	)		246,586


Total securities available-for-sale	$	2,654,885	$	84,855	$	(5,841	)	$	2,733,899

Disclosures related to the Company’s held-to-maturity securities, which totaled $121,000 and $278,000 at December 31, 2016 and 2015, respectively, have not been presented due to insignificance.

The Company invests in mortgage-backed securities that have expected maturities that differ from their contractual maturities. These differences arise because borrowers may have the right to call or prepay obligations with or without a prepayment penalty. These securities include collateralized mortgage obligations (CMOs) and other asset backed securities. The expected maturities of these securities at December 31, 2016, were computed by using scheduled amortization of balances and historical prepayment rates. At December 31, 2016 and 2015, the Company did not hold any CMOs that entail higher risks than standard mortgage-backed securities.

The amortized cost and estimated fair value of available-for-sale securities at December 31, 2016, by contractual and expected maturity, are shown below (in thousands):


	Amortized Cost Basis		Estimated Fair Value

Due within one year	$	206,182	$	207,276
Due after one year through five years		664,151		684,849
Due after five years through ten years		836,421		845,257
Due after ten years		3,360		3,658
Mortgage-backed securities		1,117,658		1,119,797

Total	$	2,827,772	$	2,860,837

The following tables disclose, as of December 31, 2016 and 2015, the Company’s investment securities that have been in a continuous unrealized-loss position for less than 12 months and for 12 or more months (in thousands):


	Less than 12 Months				12 Months or Longer				Total
December 31, 2016	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss

Obligations of state and political subdivisions	$	446,052	$	9,997	$	1,209	$	16	$	447,261	$	10,013
Corporate bonds and other		244		3		—		—		244		3
Residential mortgage-backed securities		372,331		4,532		33,227		981		405,558		5,513
Commercial mortgage-backed securities		193,495		1,180		13,263		50		206,758		1,230

Total	$	1,012,122	$	15,712	$	47,699	$	1,047	$	1,059,821	$	16,759


	Less than 12 Months				12 Months or Longer				Total
December 31, 2015	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss

U.S. Treasury securities	$	5,110	$	2	$	—	$	—	$	5,110	$	2
Obligations of U.S. government sponsored enterprises and agencies		50,388		107		—		—		50,388		107
Obligations of state and political subdivisions		32,929		127		1,513		7		34,442		134
Corporate bonds and other		7,004		5		—		—		7,004		5
Residential mortgage-backed securities		231,481		1,765		63,919		1,994		295,400		3,759
Commercial mortgage-backed securities		196,163		1,752		9,345		82		205,508		1,834

Total	$	523,075	$	3,758	$	74,777	$	2,083	$	597,852	$	5,841

The number of investments in an unrealized loss position totaled 466 at December 31, 2016. We do not believe these unrealized losses are “other-than-temporary” as (i) we do not have the intent to sell our securities prior to recovery and/or maturity and, (ii) it is more likely than not that we will not have to sell our securities prior to recovery and/or maturity. In making this determination, we also consider the length of time and extent to which fair value has been less than cost and the financial condition of the issuer. The unrealized losses noted are interest rate related due to the level of interest rates at December 31, 2016 compared to the time of purchase. We have reviewed the ratings of the issuers and have not identified any issues related to the ultimate repayment of principal as a result of credit concerns on these securities. Our mortgage related securities are backed by GNMA, FNMA and FHLMC or are collateralized by securities backed by these agencies. At December 31, 2016, 82.13% of our available-for-sale securities that are obligations of states and political subdivisions were issued within the State of Texas, of which 33.91% are guaranteed by the Texas Permanent School Fund.

Securities, carried at approximately $1,940,460,000 and $1,759,570,000 at December 31, 2016 and 2015, respectively, were pledged as collateral for public or trust fund deposits, repurchase agreements and for other purposes required or permitted by law.

During 2016, 2015, and 2014, sales of investment securities that were classified as available-for-sale totaled $40,510,000, $35,580,000 and $1,619,000. Gross realized gains from 2016, 2015, and 2014, securities sales were $1,579,000, $443,000 and $2,000, respectively. Gross realized losses from 2016, 2015 and 2014 securities sales were $309,000, $11,000 and $6,000, respectively. The specific identification method was used to determine cost in order to compute the realized gains and losses.