Mack-Cali Realty Corporation Stockholders' Equity And Mack-Cali Realty, L.P.'s Partners' Capital (Earnings Per Share Tables - Diluted 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]
Net income (loss) from continuing operations available to common shareholders	$ (24,844)	$ (36,541)
Add (deduct): Noncontrolling interests in Operating Partnership	(2,305)	(3,562)
Add (deduct): Redemption value adjustment of redeemable noncontrolling interests in the Operating Partnership unitholders	(179)	(296)
Income (loss) from continuing operations for diluted earnings per share	(27,328)	(40,399)
Income (loss) from discontinued operations for diluted earnings per share	33,743	(6,840)
Net income (loss) available for diluted earnings per share	$ 6,415	$ (47,239)
Weighted average common shares	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)
Mack-Cali Realty LP [Member]
Stockholders Equity [Line Items]
Net income (loss) from continuing operations available to common shareholders	$ (27,328)	$ (40,399)
Income (loss) from discontinued operations for diluted earnings per share	33,743	(6,840)
Net income (loss) available for diluted earnings per share	$ 6,415	$ (47,239)
Weighted average common unit	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)