|3 Months Ended|
Mar. 31, 2019
|Share-based Compensation [Abstract]|
The Company has granted restricted stock units to employees and directors pursuant to the 2013 Restated Incentive Stock Plan ("2013 Plan") as discussed below. During the three months ended March 31, 2019 and 2018, the Company’s stock-based compensation expense, which is included in general and administrative expenses in the accompanying consolidated statement of operations, was $2.8 million and $2.7 million, respectively, of which the Company capitalized $1.1 million during both the three months ended March 31, 2019 and 2018, relating to its exploration and development efforts.
The following table summarizes restricted stock unit activity for the three months ended March 31, 2019:
Restricted Stock Units
Restricted stock units awarded under the 2013 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 expense is expensed 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 March 31, 2019 related to restricted stock units was $14.8 million. The expense is expected to be recognized over a weighted average period of 2.09 years.
Performance Vesting Restricted Stock Units
During the three months ended March 31, 2019, the Company awarded performance vesting units to its Chief Executive Officer under the 2013 Plan. The number of shares of common stock that will ultimately be issued will be determined by comparing the Company's total stockholder return relative to the total stockholder return of a predetermined group of peer companies at the end of the performance period. The performance period is 36 months. The grant date fair value was determined using the Monte Carlo simulation method and is being expensed ratably over the performance period. Expected volatilities utilized in the model were estimated using a historical period consistent with the remaining performance period of approximately three years. The risk-free interest rate was based on the U.S. Treasury rate for a term commensurate with the expected life of the grant. The Company assumed a risk-free interest rate of 2.42% and a range of expected volatilities of 30.5% to 72.6% to estimate the fair value of performance vesting units granted during the three months ended March 31, 2019. Unrecognized compensation expense as of March 31, 2019 related to performance vesting restricted shares was $2.2 million. The expense is expected to be recognized over a weighted average period of 2.76 years.
The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef