(6)	STOCK-BASED COMPENSATION

The Company adopted a nonqualified incentive stock option plan (the “BancFirst ISOP”) in May 1986. The Company has amended the BancFirst ISOP since 1986 to increase the number of shares to be issued under the plan to 6,400,000 shares. At March 31, 2018, there were 309,970 shares available for future grants. The BancFirst ISOP will terminate on December 31, 2019, if not extended. The options vest and are exercisable beginning four years from the date of grant at the rate of 25% per year for four years. Options expire at the end of fifteen years from the date of grant. Options outstanding as of March 31, 2018 will become exercisable through the year 2025. The option price must be no less than 100% of the fair value of the stock relating to such option at the date of grant.

In June 1999, the Company adopted the BancFirst Corporation Non-Employee Directors’ Stock Option Plan (the “BancFirst Directors’ Stock Option Plan”). Each non-employee director is granted an option for 10,000 shares. The Company has amended the BancFirst Directors’ Stock Option Plan since 1999 to increase the number of shares to be issued under the plan to 520,000 shares. At March 31, 2018, there were 50,000 shares available for future grants. The BancFirst Directors’ Stock Option Plan will terminate on December 31, 2019, if not extended. The options vest and are exercisable beginning one year from the date of grant at the rate of 25% per year for four years, and expire at the end of fifteen years from the date of grant. Options outstanding as of March 31, 2018 will become exercisable through the year 2022. The option price must be no less than 100% of the fair value of the stock relating to such option at the date of grant.

The Company currently uses newly issued shares for stock option exercises, but reserves the right to use shares purchased under the Company’s Stock Repurchase Program (the “SRP”) in the future.

The following table is a summary of the activity under both the BancFirst ISOP and the BancFirst Directors’ Stock Option Plan:

						Wgtd. Avg.
				Wgtd. Avg.		Remaining	Aggregate
				Exercise		Contractual	Intrinsic
	Options			Price		Term	Value
	(Dollars in thousands, except option data)
Three Months Ended March 31, 2018
Outstanding at December 31, 2017		1,273,625		$	25.90
Options granted		30,000			54.73
Options exercised		(76,950	)		16.02
Outstanding at March 31, 2018		1,226,675			27.22	10.00 Yrs	$	31,747
Exercisable at March 31, 2018		520,925			20.77	7.30 Yrs	$	16,840

The following table has additional information regarding options granted and options exercised under both the BancFirst ISOP and the BancFirst Directors’ Stock Option Plan:

	Three Months Ended March 31,
	2018		2017
	(Dollars in thousands except per share data)
Weighted average grant-date fair value per share of options granted	$	13.98	$	—
Total intrinsic value of options exercised		2,860		4,613
Cash received from options exercised		1,233		2,610
Tax benefit realized from options exercised		729		1,784

The fair value of each option grant is estimated on the date of grant using the Black-Scholes option-pricing model and is based on certain assumptions including risk-free rate of return, dividend yield, stock price volatility and the expected term. The fair value of each option is expensed over its vesting period.

The following table is a summary of the Company’s recorded stock-based compensation expense:

	Three Months Ended March 31,
	2018		2017
	(Dollars in thousands)
Stock-based compensation expense	$	306	$	222
Tax benefit		78		71
Stock-based compensation expense, net of tax	$	228	$	151

The Company will continue to amortize the unearned stock-based compensation expense over the remaining vesting period of approximately seven years. The following table shows the unearned stock-based compensation expense:

	March 31, 2018
	(Dollars in thousands)
Unearned stock-based compensation expense	$	3,444

The following table shows the assumptions used for computing stock-based compensation expense under the fair value method on options granted during the periods presented:

	Three Months Ended March 31,
	2018	2017
Risk-free interest rate	2.55 to 2.92%		—
Dividend yield	2.00%		—
Stock price volatility	23.05 to 23.18%		—
Expected term	10 Yrs		—

The risk-free interest rate is determined by reference to the spot zero-coupon rate for the U.S. Treasury security with a maturity similar to the expected term of the options. The dividend yield is the expected yield for the expected term. The stock price volatility is estimated from the recent historical volatility of the Company’s stock. The expected term is estimated from the historical option exercise experience. The Company accounts for forfeitures as they occur.

In May 1999, the Company adopted the BancFirst Corporation Directors’ Deferred Stock Compensation Plan (the “BancFirst Deferred Stock Compensation Plan”). The Company has amended the BancFirst Deferred Stock Compensation Plan since 1999 to increase the number of shares to be issued under the plan to 222,220 shares. The BancFirst Deferred Stock Compensation Plan will terminate on December 31, 2019, if not extended. Under the plan, directors and members of the community advisory boards of the Company and its subsidiaries may defer up to 100% of their board fees. They are credited for each deferral with a number of stock units based on the current market price of the Company’s stock, which accumulate in an account until such time as the director or community board member terminates serving as a board member. Shares of common stock of the Company are then distributed to the terminating director or community board member based upon the number of stock units accumulated in his or her account. There were 2,842 and 7,782 shares of common stock distributed from the BancFirst Deferred Stock Compensation Plan during the three months ended March 31, 2018 and March 31, 2017, respectively.

A summary of the accumulated stock units is as follows:

	March 31,		December 31,
	2018		2017
Accumulated stock units		137,889		138,768
Average price	$	23.34	$	22.84