In accordance with the Company’s 2013 Incentive Plan, stock awards, including stock options and restricted stock, have been granted to certain employees and non-employee directors. Shares of common stock available for distribution to satisfy the grants may consist, in whole or in part, of authorized and unissued shares, treasury shares or shares reacquired by the Company in any manner. Stock-based compensation expense related to stock awards totaled $0.3 million and $0.2 million for the nine-month periods ended September 30, 2021 and 2020, respectively.

Stock option awards have been granted with an exercise price equal to the market price of the Company’s common stock on the date of the grant and have vesting periods ranging from one to three years, with 10-year contractual terms.

The Company recognizes the cost of services received in exchange for stock option awards based on the grant date fair value of the award, with compensation expense recognized on a straight-line basis over the award’s vesting period. The fair value of outstanding awards was determined using the Black-Scholes option pricing model based on the assumptions noted in the table below. Expected volatilities are based on historical volatilities of the Company’s common stock. The Company did not grant any stock option awards during the nine months ended September 30, 2021.

The following table summarizes the Company’s stock option activity for the periods presented.

	Nine Months Ended
	September 30, 2021				September 30, 2020
	Number of Shares		Average Exercise Price		Number of Shares		Average Exercise Price
Options:
Outstanding, beginning of period		421,000	$	9.79		412,800	$	9.72
Granted		—		—		10,200		11.95
Exercised		750		8.23		666		10.75
Expired		—		—		—		—
Forfeited		—		—		1,334		9.70
Options outstanding, end of period		420,250	$	9.79		421,000	$	9.79
Options exercisable, end of period		395,678	$	9.74		359,413	$	9.62

The aggregate intrinsic value of stock options outstanding (calculated as the amount by which the market value of underlying stock exceeds the exercise price of the option) was approximately $0.6 million and zero as of September 30, 2021 and 2020, respectively.

During the nine months ended September 30, 2021 and 2020, 38,430 shares and 28,460 shares, respectively, of restricted stock were granted. The Company recognizes the cost of services received in exchange for restricted stock awards based on the grant date closing price of the stock, with compensation expense recognized on a straight-line basis over the award’s vesting period.