million.

Certain individuals and entities own common units in the Operating Partnership. A common unit and a share of Common Stock of the General Partner have substantially the same economic characteristics in as much as they effectively share equally in the net income or loss of the Operating Partnership. Common unitholders have the right to redeem their common units, subject to certain restrictions. The redemption is required to be satisfied in shares of Common Stock, cash, or a combination thereof, calculated as follows: one share of the General Partner’s Common Stock, or cash equal to the fair market value of a share of the General Partner’s Common Stock at the time of redemption, for each common unit. The General Partner, in its sole discretion, determines the form of redemption of common units (i.e., whether a common unitholder receives Common Stock, cash, or any combination thereof). If the General Partner elects to satisfy the redemption with shares of Common Stock as opposed to cash, it is obligated to issue shares of its Common Stock to the redeeming unitholder. Regardless of the rights described above, the common unitholders may not put their units for cash to the General Partner or the Operating Partnership under any circumstances. When a unitholder redeems a common unit, noncontrolling interests in the Operating Partnership is reduced and Mack-Cali Realty Corporation Stockholders’ equity is increased.

LTIP Units

On March 8, 2016, the Company granted 2016 LTIP Awards to senior management of the Company, including the General Partner’s executive officers. On April 4, 2017, the Company granted 2017 LTIP Awards to senior management of the Company, including the General Partner’s executive officers. On April 20, 2018, the Company granted 2018 LTIP Awards to senior management of the Company, including the General Partner’s executive officers. On March 22, 2019, the Company granted 2019 LTIP Awards to senior management of the Company, including the General Partner’s executive officers. On March 24, 2020, the Company granted 2020 LTIP Awards to senior management of the Company, including the General Partner’s executive officers. All of the 2016 LTIP Awards, 2017 LTIP Awards, 2018 LTIP Awards, 2019 LTIP Awards and 2020 LTIP Awards are in the form of units in the Operating Partnership. See Note 16: Mack-Cali Realty Corporation Stockholders’ Equity and Mack-Cali Realty, L.P.’s Partners’ Capital – Long-Term Incentive Plan Awards.

LTIP Units are designed to qualify as “profits interests” in the Operating Partnership for federal income tax purposes. As a general matter, the profits interests characteristics of the LTIP Units mean that initially they will not be economically equivalent in value to a common unit. If and when events specified by applicable tax regulations occur, LTIP Units can over time increase in value up to the point where they are equivalent to common units on a one-for-one basis. After LTIP Units are fully vested, and to the extent the special tax rules applicable to profits interests have allowed them to become equivalent in value to common units, LTIP Units may be converted on a one-for-one basis into common units. Common units in turn have a one-for-one relationship in value with shares of the General Partner’s common stock, and are redeemable on a one-for-one basis for cash or, at the election of the Company, shares of the General Partner’s common stock.

AO LTIP Units (Appreciation-Only LTIP Units)

On March 13, 2019, the Company granted 625,000 AO LTIP Units to Mr. DeMarco pursuant to the AO Long Term Incentive Plan Award Agreement. See Note 16: Mack-Cali Realty Corporation Stockholders’ Equity and Mack-Cali Realty, L.P.’s Partners’ Capital – AO LTIP Units (Appreciation-Only LTIP Units).

AO LTIP Units are a class of partnership interests in the Operating Partnership that are intended to qualify as “profit interests” for federal income tax purposes and generally only allow the recipient to realize value to the extent the fair market value of a share of Common Stock exceeds the threshold level set at the time the AO LTIP Units are granted, subject to any vesting conditions applicable to the award. The value of vested AO LTIP Units is realized through conversion of the AO LTIP Units into Common Units. The number of Common Units into which vested AO LTIP Units may be converted is determined based on the quotient of (i) the excess of the fair market value of the Common Stock on the conversion date over the threshold level designated at the time the AO LTIP Unit was granted, divided by (ii) the fair market value of the Common Stock on the conversion date. AO LTIP Units, once vested, have a finite term during which they may be converted into Common Units, not in excess of ten years from the grant date of the AO LTIP Units.

Unit Transactions

The following tables set forth the changes in noncontrolling interests in subsidiaries which relate to the Common Units and LTIP Units in the Operating Partnership for the three months ended June 30, 2020 and 2019, respectively.

The following tables set forth the changes in noncontrolling interests in subsidiaries which relate to the Common Units and LTIP Units in the Operating Partnership for the six months ended June 30, 2020 and 2019, respectively.

Noncontrolling Interests Ownership in Operating Partnership

As of June 30, 2020 and December 31, 2019, the noncontrolling interests common unitholders owned 9.6 percent and 9.6 percent of the Operating Partnership, respectively.