Significant Accounting Policies (Narrative) (Details) - USD ($)
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3 Months Ended |
12 Months Ended |
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Jan. 01, 2019 |
Mar. 31, 2020 |
Dec. 31, 2019 |
Mar. 31, 2019 |
Dec. 31, 2017 |
Apr. 02, 2020 |
Jan. 03, 2020 |
Dec. 31, 2018 |
| Significant Accounting Policies [Line Items] |
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| Capitalized development and construction salaries and other related costs |
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$ 500,000
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$ 600,000
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| Maximum period after cessation of major construction activity that projects are considered complete |
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1 year
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| Threshold of investment value for discontinuation of equity method accounting |
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$ 0
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| Amortization of deferred financing costs |
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1,024,000
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1,189,000
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| Leasing personnel costs |
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1,038,000
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$ 742,000
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| Deferred tax asset |
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10,100,000
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$ 5,300,000
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| Income taxes, material adjustment amount |
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$ 0
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| Common stock, shares outstanding |
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90,596,079
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90,595,176
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90,595,197
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| Common units outstanding |
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9,518,638
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9,612,064
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10,009,355
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9,488,794
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10,229,349
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| LTIP units outstanding |
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3,094,324
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1,826,331
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1,826,331
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1,949,601
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1,707,106
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| Distributions payable, record date |
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Apr. 02, 2020
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Jan. 03, 2020
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| Distributions payable, approved date |
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Mar. 23, 2020
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Dec. 17, 2019
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| Common stock dividends and common unit distributions per share |
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$ 0.20
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$ 0.20
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| Stock compensation expense |
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$ 2,530,000
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$ 1,880,000
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| Distributions payable, pay date |
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Apr. 14, 2020
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Jan. 10, 2020
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| Increase (decrease) to valuation allowance |
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$ (5,300,000)
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| Federal income tax rate |
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21.00%
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| Gain from extinguishment of debt, net |
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1,311,000
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| Net income (loss) |
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$ (37,844,000)
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275,594,000
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| Accounting Standards Update 2017-12 [Member] |
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| Significant Accounting Policies [Line Items] |
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| Net income (loss) |
$ 400,000
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| Subsequent Event [Member] |
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| Significant Accounting Policies [Line Items] |
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| Common stock, shares outstanding |
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90,596,168
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| Common units outstanding |
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9,394,754
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| LTIP units outstanding |
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3,218,208
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| Mack-Cali Realty LP [Member] |
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| Significant Accounting Policies [Line Items] |
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| Gain from extinguishment of debt, net |
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1,311,000
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| Net income (loss) |
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(37,844,000)
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$ 275,594,000
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| LTIP value |
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$ 400,000
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| Dividends paid |
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400,000
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18,100,000
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| Mack-Cali Realty LP [Member] | General Partner Common Unitholders [Member] |
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| Significant Accounting Policies [Line Items] |
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| Dividends paid |
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18,100,000
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| Common Units [Member] | Mack-Cali Realty LP [Member] | Limited Partner Common Unitholders [Member] |
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| Significant Accounting Policies [Line Items] |
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| Dividends paid |
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$ 1,900,000
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$ 1,900,000
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