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Stock-Based and Other Long-Term Incentive Compensation
 9 Months Ended
Sep. 30, 2025
Share-Based Payment Arrangement [Abstract]  
Stock-Based and Other Long-Term Incentive Compensation Stock-Based and Other Long-Term Incentive Compensation
We maintain two stockholder approved plans for the issuance of stock-based compensation awards to our employees and Board of Director members: (i) the 2019 Equity Incentive Plan, as amended (the “Equity Incentive Plan”), and (ii) the 1998 Stock Option Plan, as amended (the “Stock Option Plan”).

The following table summarizes the total stock-based compensation expense recognized during the periods presented:
Three months ended September 30, Nine months ended September 30,
2025202420252024
Equity-classified$612 $522 $1,550 $1,038 
Liability-classified (1)
139 46 276 62 
$751 $568 $1,826 $1,100 
(1)    Represents compensation expense associated with awards that may be settled in cash at the option of the grantee.

1998 Stock Option Plan
The Stock Option Plan provides for the granting of incentive and non-qualified stock options to our employees for up to 1,000,000 shares of common stock. After consideration of the activity described in the table below, a total of 392,169 shares remained available for grant under the Stock Option Plan as of September 30, 2025. The last date that grants can be made under the Stock Option Plan is February 28, 2026. A summary of all option activity during the nine months ended September 30, 2025 is presented below:
Number of Shares Underlying
Stock Options
Weighted Average
Exercise
 Price
Weighted
Average
Remaining
Contractual Life (years)
Aggregate
Intrinsic
Value
Outstanding, December 31, 2024113,751 $20.44 5.84$747 
Granted44,250 $22.34 $— 
Exercised(12,500)$13.05 $159 
Canceled/Forfeited(5,833)$23.66 $16 
Expired(23,167)$22.90 $— 
Outstanding, September 30, 2025116,501 $21.31 7.60$781 
Exercisable, September 30, 202547,751 $20.05 5.37$382 

The following table summarizes information about our stock options outstanding as of September 30, 2025:
 
Range of Exercise Prices:
Options Outstanding
Options Exercisable
Shares
Weighted
Average
Remaining
Contractual
Life (years)
Weighted
Average
Exercise
Price
Shares
Weighted
Average
Exercise
Price
$0.01-$18.00
19,501 6.58$10.82 17,835 $10.92 
$18.01-$26.00
80,750 9.10$22.46 13,666 $22.33 
$26.01-$30.00
16,250 1.38$28.15 16,250 $28.15 
116,501 7.60$21.31 47,751 $20.05 
The following table summarizes changes in our unvested stock options during the nine months ended September 30, 2025:
SharesWeighted Average Grant Date Fair Value Per Share
Unvested, December 31, 2024
48,998 $11.35 
Granted44,250 $12.07 
Vested
(20,498)$10.60 
Canceled/Forfeited(4,000)$12.46 
Unvested, September 30, 2025
68,750 $11.97 
As of September 30, 2025, there was a total of approximately $0.5 million of unrecognized compensation cost related to unvested options which is expected to be recognized over the next 2.09 years.
2019 Equity Incentive Plan
On June 5, 2025, our stockholders approved an amendment to the Equity Incentive Plan (the “Amendment”) to increase the number of shares available by 500,000 shares up to a total of 1,650,000 shares of common stock for issuance in the form of awards for: (i) stock options, (ii) stock appreciation rights, (iii) restricted awards in the form of restricted stock and restricted stock units (“RSUs”), (iv) performance share awards, including performance share units (“PSUs”) and (v) other equity-based awards. In addition, the Amendment extended the term of the Equity Incentive Plan by five years to June 20, 2034. After consideration of the activity described in detail below, a total of 635,421 shares remained available for grant under the Equity Incentive Plan as of September 30, 2025.
Time-Vested Restricted Stock and Restricted Stock Units
The following table summarizes all restricted stock and RSU activity during the nine months ended September 30, 2025 is presented below:
 Number
 of
Shares		Weighted Average
Grant Date Fair Value		Weighted
Average
Remaining
Contractual Life (years)
Aggregate
Intrinsic
Value
Outstanding, December 31, 2024131,183 $16.39 5.15$3,516 
Granted75,031 $22.78 $1,709 
Vested(72,874)$15.13 $1,796 
Canceled/Forfeited(910)$22.19 $17 
Outstanding, September 30, 2025132,430 $20.66 4.15$3,707 
As of September 30, 2025, there was a total of approximately $1.9 million of unrecognized compensation cost related to unvested restricted stock and RSUs which is expected to be recognized over the next 1.98 years.
Cash Settled Restricted Stock Units
The 2025 and 2024 grants of RSUs to the independent Board members that can be settled in cash represent liability-classified awards. Compensation expense associated with these awards is based upon the fair value of NGS common stock at each reporting period relative to that portion of the service period that has passed. Accordingly, the compensation expense is variable in nature.
 Number
 of
Shares		Weighted Average
Grant Date Fair Value		Weighted
Average
Remaining
Contractual Life (years)
Aggregate
Intrinsic
Value
Outstanding, Outstanding, December 31, 202415,069 $19.51 0.50$294 
Granted13,812 $24.60 $340 
Vested(10,527)$19.57 $206 
Canceled/Forfeited(2,810)$19.57 $55 
Outstanding, September 30, 202515,544 $23.99 0.61$414 
Performance Share Units
The potential payout for the PSU awards is based upon performance for a three-year period ending December 31, 2026 for the 2024 grants and December 31, 2027 for the 2025 grants measured against relative total shareholder return (“TSR”) compared to a peer group of companies as established by the Compensation Committee. The PSU award payout ranges from zero (if the Company ranks below the 31.25 percentile) and up to 200% (if the Company ranks first) based upon our relative TSR performance ranking (subject to certain caps based on absolute TSR as defined in the PSU agreements).
With respect to vesting, the PSUs have both a service condition and a market condition. Due to the presence of the TSR measurement for the common equity of the peer companies, including NGS common stock, which is deemed a “market condition,” the grant-date fair values of the PSUs have been determined using a binomial pricing model, or a Monte Carlo simulation model.
The following table summarizes the weighted average grant date fair values of PSUs granted and the assumptions used in the Monte Carlo simulation model for the determination of the grant date fair values of our PSUs granted during the nine months ended September 30, 2025:
Weighted-average grant date fair value of PSUs granted$28.22 
Risk free rate3.91 %
Expected volatility44.0 %
Expected dividend yield— %
The following table summarizes all PSU activity during the nine months ended September 30, 2025:
Number
 of
Shares		Weighted Average
Grant Date Fair Value		Weighted
Average
Remaining
Contractual Life (years)		Aggregate
Intrinsic
Value
Outstanding, December 31, 202456,764 $22.47 2.22$— 
Granted41,724 $28.22 $— 
Vested— $— 
Canceled/Forfeited— $— 
Outstanding, September 30, 202598,488 $24.91 1.89$— 
As of September 30, 2025, there was a total of approximately $1.6 million of unrecognized compensation cost related to the unvested portion of the PSUs which is expected to be recognized over the next 1.89 years.