|9 Months Ended
Sep. 30, 2019
|Share-based Payment Arrangement, Noncash Expense [Abstract]
The Company has granted restricted stock units to employees and directors pursuant to the 2019 Amended and Restated Incentive Stock Plan ("2019 Plan"), as discussed below. During the three and nine months ended September 30, 2019, the Company’s stock-based compensation cost was $2.7 million and $8.3 million, respectively, of which the Company capitalized $1.1 million and $3.3 million, respectively, relating to its exploration and development efforts. During the three and nine months ended September 30, 2018, the Company's stock-based compensation cost was $3.6 million and $9.7 million, respectively, of which the Company capitalized $1.4 million and $3.9 million, respectively, relating to its exploration and development efforts. Stock compensation costs, net of the amounts capitalized, are included in general and administrative expenses in the accompanying consolidated statements of operations.
The following table summarizes restricted stock unit activity for the nine months ended September 30, 2019:
Restricted Stock Units
Restricted stock units awarded under the 2019 Plan generally vest over a period of one year in the case of directors and three years in the case of employees and vesting is dependent upon the recipient meeting applicable service requirements. Stock-based compensation costs are recorded ratably over the service period. The grant date fair value of restricted stock units represents the closing market price of the Company's common stock on the date of grant. Unrecognized compensation expense as of September 30, 2019 related to restricted stock units was $19.0 million. The expense is expected to be recognized over a weighted average period of 2.28 years.
Performance Vesting Restricted Stock Units
During the nine months ended September 30, 2019, the Company awarded performance vesting units to certain of its executive officers under the 2019 Plan. The number of shares of common stock issued pursuant to the award will be based on relative total shareholder return ("RTSR"). RTSR is an incentive measure whereby participants will earn from 0% to 200% of the target award based on the Company’s RTSR ranking compared to the RTSR of the companies in the Company’s designated peer group at the end of the performance period. Awards will be earned and vested over a performance period measured from January 1, 2019 to December 31, 2021, subject to earlier termination of the performance period in the event of a change in control. The grant date fair value was determined using the Monte Carlo simulation method and is being recorded ratably over the performance period. Expected volatilities utilized in the Monte Carlo model were estimated using a historical period consistent with the remaining performance period of approximately two years. The risk-free interest rates were based on the U.S. Treasury rate for a term commensurate with the expected life of the grant. The Company assumed a range of risk-free interest rates of 1.56% to 2.42% and a range of expected volatilities of 29.1% to 85.1% to estimate the fair value of performance vesting units granted during the nine months ended September 30, 2019. Unrecognized compensation expense as of September 30, 2019 related to performance vesting restricted shares was $4.9 million. The expense is expected to be recognized over a weighted average period of 2.64 years.