The Company’s stock-incentive program is a long-term retention program that is intended to attract, retain and provide incentives for talented employees, officers and directors, and to align stockholder and employee interests. Currently, the Company is able to grant options, SARs and restricted shares from the Amended 2004 Plan. Unless earlier terminated by action of the Board, the Amended 2004 Plan will remain in effect until such time as no stock remains available for delivery and the Company has no further rights or obligations under the Amended 2004 Plan with respect to outstanding awards thereunder.

Historically, stock options have been granted with an exercise price equal to the market value of the common stock on the date of grant, expire 10 years from the date they are granted, and generally vested over a one to three-year period for members of the Board of Directors and a one to three-year period for employees. Upon exercise, new shares can be issued by the Company. The Company granted stock options in 2018 which vest one-third each year on the anniversary of the grant date. The Company granted stock options in 2017 which vested monthly over a one-year period. SARs are generally granted with a grant price equal to the market value of the common stock on the date of grant, vest one-third each year on the anniversary of the date of grant and expire five years from the date of grant. The restricted shares and restricted stock units granted to employees generally have a three-year graded vesting period and are subject to accelerated vesting and forfeiture under certain circumstances. Restricted shares and restricted stock units granted to board members generally have a three-year graded vesting period and are subject to accelerated vesting and forfeiture under certain circumstances.

The Company primarily uses the Black-Scholes option-pricing model to determine the fair value of stock options and SARs. The determination of the fair value of stock-based payment awards on the date of grant using an option-pricing model is affected by the Company’s stock price as well as assumptions regarding a number of complex and subjective variables. These variables include the Company’s expected stock price volatility over the term of the awards, actual and projected employee stock option exercise behaviors, risk-free interest rate and expected dividends. Expected volatility is based on historical volatility. As there is no trading volume for the Company’s options, implied volatility is not representative of the Company’s current volatility so the historical volatility of the Company’s common stock is determined to be more indicative of the Company’s expected future stock performance. The expected life is determined using the safe-harbor method. The Company expects to use this simplified method for valuing employee options and SARs grants until more detailed information about exercise behavior becomes available over time. The Company bases the risk-free interest rate on U.S. Treasury zero-coupon issues with remaining terms similar to the expected term on the options or SARs. The Company does not anticipate paying any cash dividends in the foreseeable future and therefore uses an expected dividend yield of zero in the option valuation model. The Company is required to estimate forfeitures at the time of grant and revise those estimates in subsequent periods if actual forfeitures differ from those estimates. The Company uses historical data to estimate pre-vesting option forfeitures and records stock-based compensation expense only for those awards that are expected to vest. The Company recognizes compensation cost, net of estimated forfeitures, arising from the issuance of stock options and SARs on a straight-line basis over the vesting period of the grant.

The estimated compensation cost associated with the granting of restricted stock and restricted stock units is based on the fair value of the Company’s common stock on the date of grant. The Company recognizes the compensation cost, net of estimated forfeitures, arising from the issuance of restricted stock and restricted stock units on a straight-line basis over the shorter of the vesting period or the period from the grant date to the date when retirement eligibility is achieved.

The following table provides the weighted average assumptions used in determining the fair value of the stock options granted during the years ended December 31, 2018 and December 31, 2017.

The weighted-average fair value of stock options granted during the year ended December 31, 2018 was estimated to be $0.93. The weighted-average fair value of stock options granted during the year ended December 31, 2017 was estimated to be $1.49. There were no options or SARs exercised in 2018 or 2017. Historically, shares issued upon the exercise of options have been new shares and have not come from treasury shares.

The impact of RSUs and stock options on net loss for the years ended December 31, 2018 and 2017 is as follows:

A summary of stock option and SARs activity for the year ended December 31, 2018, and changes during such year, is presented below:

A summary of the status of the Company’s non-vested options for the year ended December 31, 2018, and changes during such year, is presented below:

The aggregate fair value of SARs and options vested during the years ended December 31, 2018 and 2017 was $1.2 million and $1.1 million, respectively. The weighted-average grant date fair value of options vested during the year ended December 31, 2017 was $1.61.

A summary of the Company’s non-vested shares of restricted stock units for the year ended December 31, 2018, and changes during such year, is presented below:

The aggregate fair value of restricted stock units vested during each of the years ended December 31, 2018 and 2017 was $0.1 million, respectively in both periods.

As of December 31, 2018, there was approximately $1.1 million of total unrecognized compensation cost, net of estimated forfeitures, related to unvested stock options and restricted stock units.