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	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stockolders Equity [Line Items]
Net income (loss) from continuing operations available to common shareholders									$ 184,273,000	$ 49,213,000	$ (15,274,000)
Net income available to common shareholders									252,554,000	80,267,000	10,840,000
Add (deduct): Noncontrolling interests in Operating Partnership									23,685,000	6,866,000	341,000
Add (deduct): Redemption value adjustment of redeemable noncontrolling interests in Operating Partnership unitholders									(2,855,000)	(1,296,000)	(2,074,000)
Income (loss) from continuing operations for diluted earnings per share									205,103,000	54,783,000	(17,007,000)
Income from discontinued operations for diluted earnings per share									(108,718,000)	26,134,000	22,878,000
Net income (loss) available for diluted earnings per share									$ 96,385,000	$ 80,917,000	$ 5,871,000
Weighted average common shares									100,689	100,724	100,703
Income (loss) from continuing operations available to common shareholders	$ 0.53	$ (0.64)	$ (0.45)	$ 2.58	$ 0.37	$ (0.12)	$ (0.13)	$ 0.42	$ 2.03	$ 0.54	$ (0.17)
Income from discontinued operations available to common shareholders	(1.17)	(0.01)	0.02	0.08	0.08	0.07	0.08	0.03	(1.08)	0.26	0.23
Net income (loss) available to common shareholders	(0.64)	(0.65)	(0.43)	2.66	0.45	(0.05)	(0.05)	0.45	$ 0.95	$ 0.80	$ 0.06
Mack-Cali Realty LP [Member]
Stockolders Equity [Line Items]
Net income available to common shareholders									$ 252,554,000	$ 80,267,000
Income (loss) from continuing operations for diluted earnings per share									205,103,000	54,783,000	$ (17,007,000)
Income from discontinued operations for diluted earnings per share									(108,718,000)	26,134,000	22,878,000
Net income (loss) available for diluted earnings per share									$ 96,385,000	$ 80,917,000	$ 5,871,000
Weighted average common unit									100,689	100,724	100,703
Income (loss) from continuing operations available to common shareholders	0.53	(0.64)	(0.45)	2.58	0.37	(0.12)	(0.13)	0.42	$ 2.03	$ 0.54	$ (0.17)
Income from discontinued operations available to common shareholders	(1.17)	(0.01)	0.02	0.08	0.08	0.07	0.08	0.03	(1.08)	0.26	0.23
Net income (loss) available to common shareholders	$ (0.64)	$ (0.65)	$ (0.43)	$ 2.66	$ 0.45	$ (0.05)	$ (0.05)	$ 0.45	$ 0.95	$ 0.80	$ 0.06