We issue service-based restricted stock units (“Service RSUs”), service and performance-based restricted stock units (“Performance RSUs”) and nonqualified stock options (“Options”) to certain employees and directors. We recognized share-based compensation expense of $6 million and $5 million during the three months ended September 30, 2019 and 2018, respectively, and $18 million and $13 million for the nine months ended September 30, 2019 and 2018, respectively. As of September 30, 2019, unrecognized compensation costs for unvested awards were approximately $23 million, which is expected to be recognized over a weighted average period of 1.9 years. As of September 30, 2019, there were 6,485,046 shares of common stock available for future issuance under this plan.

During the nine months ended September 30, 2019, we issued 500,925 Service RSUs with a weighted-average grant date fair value of $33.07, which generally vest in equal annual installments over three years from the date of grant.

During the nine months ended September 30, 2019, we issued 544,209 Options with a weighted-average exercise price of $33.32, which vest over three years from the date of the grant.

The weighted-average grant date fair value of these options was $12.29, which was determined using the Black-Scholes-Merton option-pricing model with the following assumptions:

Expected volatility	33.1	%
Dividend yield	—	%
Risk-free rate	2.6	%
Expected term (in years)	6.0

As of September 30, 2019, we had 624,145 Options outstanding that were exercisable.

During the nine months ended September 30, 2019, we issued 133,660 Performance RSUs with a weighted-average grant date fair value of $33.32. The Performance RSUs are settled at the end of a three-year performance period, with 70 percent of the Performance RSUs subject to achievement based on the Company’s adjusted earnings before interest expense, taxes and depreciation and amortization further adjusted for net deferral and recognition of revenues and related direct expenses related to sales of VOIs of projects under construction. The remaining 30 percent of the Performance RSUs are subject to the achievement of certain contract sales targets. We determined that the performance conditions for these awards are probable of achievement and, as of September 30, 2019, we recognized compensation expense based on the number of Performance RSUs we expect to vest.