Mack-Cali Realty Corporation Stockholders' Equity And Mack-Cali Realty, L.P.'s Partners' Capital (Earnings Per Share Tables - Basic Computation Of EPS) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Stockholders Equity [Line Items]
Income (loss) from continuing operations	$ (20,222)	$ (31,004)
Add (deduct): Noncontrolling interests in consolidated joint ventures	1,335	176
Add (deduct): Noncontrolling interests in Operating Partnership	2,305	3,562
Add (deduct): Redeemable noncontrolling interests	(6,471)	(6,471)
Add (deduct): Redemption value adjustment of redeemable noncontrolling interests attributable to common shareholders	(1,791)	(2,804)
Income (loss) from continuing operations available to common shareholders	(24,844)	(36,541)
Income (loss) from discontinued operations available to common shareholders	30,676	(6,187)
Net income (loss) available to common shareholders for basic earnings per share	$ 5,832	$ (42,728)
Weighted average common shares	90,692	90,616
Income (loss) from continuing operations available to common shareholders	$ (0.28)	$ (0.40)
Income (loss) from discontinued operations available to common shareholders	0.34	(0.07)
Net income (loss) available to common shareholders	$ 0.06	$ (0.47)
Mack-Cali Realty LP [Member]
Stockholders Equity [Line Items]
Income (loss) from continuing operations	$ (20,222)	$ (31,004)
Add (deduct): Noncontrolling interests in consolidated joint ventures	1,335	176
Add (deduct): Redeemable noncontrolling interests	(6,471)	(6,471)
Add (deduct): Redemption value adjustment of redeemable noncontrolling interests attributable to common shareholders	(1,970)	(3,100)
Income (loss) from continuing operations available to common shareholders	(27,328)	(40,399)
Income (loss) from discontinued operations available to common shareholders	33,743	(6,840)
Net income (loss) available to common shareholders for basic earnings per share	$ 6,415	$ (47,239)
Weighted average common units	99,760	100,183
Income (loss) from continuing operations available to common shareholders	$ (0.28)	$ (0.40)
Income (loss) from discontinued operations available to common shareholders	0.34	(0.07)
Net income (loss) available to common shareholders	$ 0.06	$ (0.47)