(15) Stock Options

On April 5, 2012, the Board of Directors adopted the 2012 International Bancshares Corporation Stock Option Plan (the “2012 Plan”). There are 800,000 shares available for stock option grants under the 2012 Plan. Under the 2012 Plan, both qualified incentive stock options (“ISOs”) and non‑qualified stock options (“NQSOs”) may be granted. Options granted may be exercisable for a period of up to 10 years from the date of grant, excluding ISOs granted to 10% shareholders, which may be exercisable for a period of up to only five years. As of December 31, 2015, 178,250 shares were available for future grants under the 2012 Plan.

The fair value of each option award granted under the plan is estimated on the date of grant using a Black‑Scholes‑Merton option valuation model that uses the assumptions noted in the following table. Expected volatility is based on the historical volatility of the price of the Company’s stock. The Company uses historical data to estimate the expected dividend yield and employee termination rates within the valuation model. The expected term of options is derived from historical exercise behavior. The risk‑free rate for periods within the contractual life of the option is based on the U.S. Treasury yield curve in effect at the time of grant.


	2015		2014
Expected Life (Years)	7.61		7.63
Dividend yield	2.36	%	2.01	%
Interest rate	1.91	%	2.28	%
Volatility	46.52	%	47.36	%

A summary of option activity under the stock option plans for the twelve months ended December 31, 2015 is as follows:


				Weighted
		Weighted		average
		average		remaining	Aggregate
	Number of	exercise		contractual	intrinsic
	options	price		term (years)	value ($)
					(in Thousands)
Options outstanding at December 31, 2014	993,889	$	18.94
Plus: Options granted	56,500		24.24
Less:
Options exercised	82,241		17.15
Options expired	44,075		26.73
Options forfeited	52,346		18.52
Options outstanding at December 31, 2015	871,727		19.08	6.66	$	5,769
Options fully vested and exercisable at December 31, 2015	212,821	$	13.99	3.38	$	2,492

Stock‑based compensation expense included in the consolidated statements of income for the years ended December 31, 2015, 2014 and 2013 was approximately $1,172,000, $1,058,000 and $414,000, respectively. As of December 31, 2015, there was approximately $3,334,000 of total unrecognized stock‑based compensation cost related to non‑vested options granted under the Company plans that will be recognized over a weighted average period of 2.0 years.

Other information pertaining to option activity during the twelve month period ending December 31, 2015, 2014 and 2013 is as follows:


	Twelve Months Ended December 31,
	2015		2014		2013
Weighted average grant date fair value of stock options granted	$	9.42	$	9.07	$	9.05
Total fair value of stock options vested	$	872,000	$	376,000	$	480,000
Total intrinsic value of stock options exercised	$	781,000	$	468,000	$	171,000