The Company’s general and administrative expenses include equity-based compensation costs related to the Antero Midstream GP LP Long-Term Incentive Plan (“AMGP LTIP”) and the Series B Units prior to the Transactions. Equity-based compensation after the Transactions include (i) costs allocated to Antero Midstream Partners by Antero Resources for grants made prior to the Transactions pursuant to Antero Resources’ long-term incentive plan, (ii) costs due to Antero Midstream Corporation LTIP (the “AMC LTIP”) and (iii) the Exchanged B Units (as defined below). Antero Midstream Partners’ portion of the equity-based compensation expense is included in general and administrative expenses, and recorded as a credit to the applicable classes of equity. Equity-based compensation expense allocated to Antero Midstream Partners was $4.9 million for the period from March 13, 2019 to December 31, 2019. For grants made prior to the Transactions, Antero Resources has total unamortized expense related to its various equity-based compensation plans that can be allocated to the Company of approximately $26 million as of December 31, 2019, which includes grants made under the AMP LTIP (as defined below) prior to the Transactions, which were converted into awards under the AMC LTIP. A portion of this will be allocated to Antero Midstream Partners as it is amortized over the remaining service period of the related awards. Antero Midstream Partners does not reimburse Antero Resources for noncash equity compensation allocated to it for awards issued under the Antero Resources long-term incentive plan.

As of December 31, 2018, IDR Holdings had 98,600 Series B Units authorized and outstanding that entitled the holders to receive up to 6% of the amount of the distributions that Antero Midstream Partners made on its incentive distribution rights (“IDRs”) in excess of $7.5 million per quarter, subject to certain vesting conditions. On December 31, 2018, 65,745 Series B Units were vested. The holders of vested Series B Units had the right to convert the units to common shares with a value equal to their pro rata share of up to 6% of any increase in AMGP’s equity value in excess of $2.0 billion.

Upon Closing of the Transactions, each Series B Unit, vested and unvested, was exchanged for 176.0041 shares of our common stock (the “Series B Exchange”). A total of 17,353,999 shares of AMC common stock were issued in exchange for the 98,600 Series B Units then outstanding (the “Exchanged B Units”), which included 5,782,601 restricted shares of AMC common stock issued in exchange for the 32,855 unvested Series B Units.

The Company accounted for the Series B Exchange as a share-based payment modification under ASC 718, Stock Compensation. On March 12, 2019, which is the modification date, the Company determined the estimated fair value of the unvested Series B Unit awards using a Monte Carlo simulation using various assumptions including a floor equity value of $2.0 billion, expected volatility of 40% based on historical volatility of a peer group of publicly traded partnerships, a risk free rate of 2.51%, and expected IDR distributions based on internal estimates discounted based on a weighted average cost of capital assumption of 7.25%. Based on these assumptions, the estimated value of each Series B Unit was $1,257 when exchanged for shares of AMC common stock. The fair value measurement is based on significant inputs not observable in the market and thus represents a Level 3 measurement within the fair value hierarchy. The unvested Exchanged B Units retained the same vesting conditions as the Series B Units and vested on December 31, 2019. No awards were issued and outstanding as of December 31, 2019. Expenses related to Exchanged B Units were recognized on a straight-line basis over the requisite service period of the entire award. Forfeitures were accounted for as they occur by reversing the expense previously recognized for awards that were forfeited during the period.

The Company recognized $66 million of equity-based compensation expense related to the Series B awards, including the Series B Units prior to the Closing of the Transactions and the Exchanged B Units following the Closing of the Transactions, for the year ended December 31, 2019. For the years ended December 31, 2017 and 2018, the Company recognized $35 million and $34 million, respectively, of equity-based compensation expense related to the Series B Units. As of December 31, 2019, there is no unamortized expense related to these awards.

On April 17, 2017, Antero Midstream GP LP adopted the AMGP LTIP pursuant to which certain non-employee directors of Antero Midstream GP LP’s general partner and certain officers, employees and consultants of Antero Resources were eligible to receive awards representing equity interests in Antero Midstream GP LP. For the years ended December 31, 2017, 2018 and 2019, the Company recognized expense of $0.2 million, $0.7 million and $0.2 million, respectively, related to these awards. Expenses related to these awards were recognized on a straight-line basis over the requisite service period of the entire award. Forfeitures were accounted for as they occur by reversing the expense previously recognized for awards that were forfeited during the period. In connection with the Transactions, the AMGP LTIP was terminated on March 12, 2019.

Effective March, 12, 2019, the Board of Directors of Antero Midstream Corporation (the “Board”) adopted the AMC LTIP under which awards may be granted to employees, directors and other service providers of the Company and its affiliates. The AMC LTIP provides for the grant of stock options, stock appreciation rights, restricted stock, restricted stock units, dividend equivalents, other stock-based awards, cash awards and substitute awards. The terms and conditions of the awards granted are established by the compensation committee of the Board. The Company is authorized to grant up to 15,398,901 shares of common stock to employees and directors under the AMC LTIP. As of December 31, 2019, a total of 13,596,444 shares were available for future grant under the AMC LTIP. For the year ended December 31, 2019, the Company recognized expense of $2.7 million related to these awards. Expenses related to restricted stock units are recognized on a straight-line basis over the requisite service period of the entire award. Forfeitures are accounted for as they occur by reversing the expense previously recognized for awards that were forfeited during the period.

As part of the Transactions, each of the unvested outstanding phantom units in the Antero Midstream Partners Long Term Incentive Plan (“AMP LTIP”) was assumed by Antero Midstream Corporation and converted into 1.8926 restricted stock units under the AMC LTIP representing a right to receive shares of AMC common stock for each converted phantom unit.

Restricted stock unit (“RSU”) awards vest subject to the satisfaction of service requirements. Expense related to each RSU award is recognized on a straight-line basis over the requisite service period of the entire award. Forfeitures are accounted for as they occur by reversing the expense previously recognized for awards that were forfeited during the period. The grant date fair values of these awards are determined based on the closing price of Antero’s common stock on the date of the grant.

A summary of RSU awards activity during the year ended December 31, 2019 is as follows:

⁽¹⁾

Effective as of March 12, 2019, all unvested outstanding phantom units in the AMP LTIP were assumed by the Company and converted into restricted stock units under the AMC LTIP at a conversion rate of 1.8926 restricted stock units for each phantom unit.

Intrinsic values are based on the closing price of the Company’s common shares on the referenced dates. At December 31,

2019, unamortized expense of $13 million related to the unvested RSUs is expected to be recognized over a weighted average period of approximately 2.5 years and the Company’s proportionate share will be allocated to it as it is recognized.

Performance Share Unit Awards Based on Return on Invested Capital (“ROIC”)

In 2019, the Company granted performance share units (“PSUs”) to certain of its employees and executive officers, a portion of which vest based on the Company’s actual ROIC (as defined in the award agreement) over a three-year period as compared to a targeted ROIC (“ROIC PSUs”). The number of shares of common stock that may ultimately be earned with respect to the ROIC PSUs ranges from zero to 200% of the target number of ROIC PSUs originally granted. Expense related to the ROIC PSUs is recognized based on the number of shares of common stock that are expected to be issued at the end of the measurement period, and such expense is reversed if the likelihood of achieving the performance condition decreases.

On December 17, 2019, the compensation committee of the Board modified the terms for the ROIC PSU agreement. Accordingly, the Company accounted for the amended agreement as a share-based payment modification under ASC 718, Stock Compensation and revalued the awards as of the modification date. Expense for the awards are recognized on a straight-line basis over the requisite service period of the entire award. For the year ended December 31, 2019, the Company recognized $0.2 million of expense related to these awards.

Summary Information for Performance Share Unit Awards

A summary of PSU activity for the year ended December 31, 2019 is as follows:


		Weighted
		Average
	Number of	grant date
	units	fair value
Total awarded and unvested—December 31, 2018	—	$	—
Granted	164,196	$	6.32
Vested	—	$	—
Forfeited	(15,890)	$	6.32
Total awarded and unvested—December 31, 2019	148,306	$	6.32

The grant-date fair value for the ROIC PSUs is based on the closing price of the Company’s common stock on the date of the modified terms for the ROIC PSU agreement, assuming the achievement of the performance condition.

As of December 31, 2019, there was $0.7 million of unamortized equity-based compensation expense related to unvested PSUs that is expected to be recognized over a weighted average period of 2.3 years.