Restricted Stock Units

During the three months ended March 31, 2019, the Company issued 15,000 restricted stock units ("RSUs") to each of its three non-management directors as an annual grant for 2019 for service on the Company's Board of Directors. The RSUs vest in four equal quarterly installments of 3,750 shares of common stock on March 15, 2019, June 15, 2019, September 15, 2019 and December 15, 2019, subject to continued service on the Board of Directors.

During the three months ended March 31, 2018, the Company issued 15,000 RSUs to each of its three non-management directors as an annual grant for 2018 for service on the Company's Board of Directors.  The RSUs vested in four equal quarterly installments of 3,750 shares of common stock on March 15, 2018, June 15, 2018, September 15, 2018 and December 15, 2018, subject to continued service on the Board of Directors.

A summary of restricted stock unit activity for the three months ended March 31, 2019 is as follows (each restricted stock unit issued by the Company represents the right to receive one share of the Company's common stock):

Restricted stock unit compensation expense was $144,000 and $226,000 for the three months ended March 31, 2019 and March 31, 2018, respectively.

The Company has an aggregate of $599,000 of unrecognized restricted stock unit compensation as of March 31, 2019 to be expensed over a weighted average period of 1.41 years.

All of the Company's outstanding (unvested) restricted stock units have dividend equivalent rights.  As of March 31, 2019, there was $102,000 accrued for dividend equivalent rights.  As of December 31, 2018, there was $76,000 accrued for dividend equivalent rights.

Stock Options

There were no stock option grants during the three months ended March 31, 2019 and March 31, 2018.

The following table presents information relating to all stock options outstanding and exercisable at March 31, 2019:

The Company had no recorded stock-based compensation related to stock option grants for the three months ended March 31, 2019 and March 31, 2018.

The Company had no unrecognized stock-based compensation cost as of March 31, 2019.  The aggregate intrinsic value of options exercisable at March 31, 2018 was $2,226,000.

During the three months ended March 31, 2019, stock options to purchase an aggregate of 105,000 shares of the Company's common stock, at an exercise price of $1.65 per share, were exercised on a net exercise (cashless) basis by three non-management directors of the Company.  With respect to the aforementioned stock options, net shares of an aggregate of 35,884 were delivered to the three non-management directors.

During the three months ended March 31, 2018, stock options to purchase an aggregate of 75,000 shares of the Company's common stock, at an exercise price of $1.19 per share, were exercised (50,000 shares of which were exercised on a net exercise (cashless) basis) by three non-management directors of the Company.  With respect to the aforementioned stock options to purchase 50,000 shares on a net exercise basis by two directors of the Company, net shares of an aggregate of 26,890 were delivered to the directors.