Consolidated Statements Of Operations - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
REVENUES
Revenue from leases	$ 296,142,000	$ 317,783,000	$ 403,635,000
Total revenues	350,935,000	365,714,000	459,030,000
EXPENSES
Real estate taxes	43,998,000	44,389,000	62,035,000
Utilities	17,881,000	23,799,000	29,493,000
Operating services	69,641,000	70,074,000	77,634,000
Real estate services expenses	15,918,000	17,919,000	23,394,000
Leasing personnel costs	2,261,000
General and administrative	57,535,000	53,865,000	50,475,000
Depreciation and amortization	132,016,000	112,244,000	142,319,000
Land and other Impairments	32,444,000	24,566,000
Total expenses	371,694,000	346,856,000	385,350,000
OTHER (EXPENSE) INCOME
Interest expense	(90,569,000)	(77,346,000)	(84,523,000)
Interest and other investment income (loss)	2,412,000	3,219,000	2,690,000
Equity in earnings (loss) of unconsolidated joint ventures	(1,319,000)	(127,000)	(6,081,000)
Gain on change of control of interests	13,790,000	14,217,000
Realized gains (losses) and unrealized losses on disposition of rental property, net	345,926,000	99,436,000	2,364,000
Gain (loss) on disposition of developable land	522,000	30,939,000
Gain on sale of investment in unconsolidated joint venture	903,000		23,131,000
Gain (loss) from extinguishment of debt, net	1,648,000	(8,929,000)	(421,000)
Total other income (expense)	273,313,000	61,409,000	(62,840,000)
Income from continuing operations	252,554,000	80,267,000	10,840,000
Discontinued operations:
Income from discontinued operations	27,456,000	26,134,000	22,878,000
Realized gains (losses) and unrealized losses on disposition of rental property and impairments, net	(136,174,000)
Total discontinued operations, net	(108,718,000)	26,134,000	22,878,000
Net income	143,836,000	106,401,000	33,718,000
Noncontrolling interests in consolidated joint ventures	3,904,000	1,216,000	1,018,000
Noncontrolling interests in Operating Partnership of income from continuing operations	(23,685,000)	(6,866,000)	(341,000)
Noncontrolling interests in Operating Partnership in discontinued operations	10,421,000	(2,661,000)	(2,370,000)
Redeemable noncontrolling interests	(22,615,000)	(13,979,000)	(8,840,000)
Net income available to common shareholders	$ 111,861,000	$ 84,111,000	$ 23,185,000
Basic earnings per common share:
Income from continuing operations	$ 2.03	$ 0.54	$ (0.17)
Discontinued operations	(1.08)	0.26	0.23
Net income available to common unitholders	0.95	0.80	0.06
Diluted earnings per common share:
Income from continuing operations	2.03	0.54	(0.17)
Discontinued operations	(1.08)	0.26	0.23
Net income available to common unitholders	$ 0.95	$ 0.80	$ 0.06
Basic weighted average shares outstanding	90,557	90,388	90,005
Diluted weighted average shares outstanding	100,689	100,724	100,703
Real Estate Services [Member]
REVENUES
Total revenues	$ 13,873,000	$ 17,094,000	$ 23,125,000
Parking Income [Member]
REVENUES
Total revenues	21,857,000	21,907,000	20,050,000
Hotel Income [Member]
REVENUES
Total revenues	9,841,000
Other Income [Member]
REVENUES
Total revenues	9,222,000	8,930,000	12,220,000
Mack-Cali Realty LP [Member]
REVENUES
Revenue from leases	296,142,000	317,783,000	403,635,000
Total revenues	350,935,000	365,714,000	459,030,000
EXPENSES
Real estate taxes	43,998,000	44,389,000	62,035,000
Utilities	17,881,000	23,799,000	29,493,000
Operating services	69,641,000	70,074,000	77,634,000
Real estate services expenses	15,918,000	17,919,000	23,394,000
Leasing personnel costs	2,261,000
General and administrative	57,535,000	53,865,000	50,475,000
Depreciation and amortization	132,016,000	112,244,000	142,319,000
Land and other Impairments	32,444,000	24,566,000
Total expenses	371,694,000	346,856,000	385,350,000
OTHER (EXPENSE) INCOME
Interest expense	(90,569,000)	(77,346,000)	(84,523,000)
Interest and other investment income (loss)	2,412,000	3,219,000	2,690,000
Equity in earnings (loss) of unconsolidated joint ventures	(1,319,000)	(127,000)	(6,081,000)
Gain on change of control of interests	13,790,000	14,217,000
Realized gains (losses) and unrealized losses on disposition of rental property, net	345,926,000	99,436,000	2,364,000
Gain (loss) on disposition of developable land	522,000	30,939,000
Gain on sale of investment in unconsolidated joint venture	903,000		23,131,000
Gain (loss) from extinguishment of debt, net	1,648,000	(8,929,000)	(421,000)
Total other income (expense)	273,313,000	61,409,000	(62,840,000)
Income from continuing operations	252,554,000	80,267,000
Discontinued operations:
Income from discontinued operations	27,456,000	26,134,000	22,878,000
Realized gains (losses) and unrealized losses on disposition of rental property and impairments, net	(136,174,000)
Total discontinued operations, net	(108,718,000)	26,134,000	22,878,000
Net income	143,836,000	106,401,000	33,718,000
Noncontrolling interests in consolidated joint ventures	3,904,000	1,216,000	1,018,000
Redeemable noncontrolling interests	(22,615,000)	(13,979,000)	(8,840,000)
Net income available to common shareholders	$ 125,125,000	$ 93,638,000	$ 25,896,000
Basic earnings per common share:
Income from continuing operations	$ 2.03	$ 0.54	$ (0.17)
Discontinued operations	(1.08)	0.26	0.23
Net income available to common unitholders	0.95	0.80	0.06
Diluted earnings per common share:
Income from continuing operations	2.03	0.54	(0.17)
Discontinued operations	(1.08)	0.26	0.23
Net income available to common unitholders	$ 0.95	$ 0.80	$ 0.06
Basic weighted average units outstanding	100,520	100,634	100,410
Diluted weighted average units outstanding	100,689	100,724	100,703
Mack-Cali Realty LP [Member] | Real Estate Services [Member]
REVENUES
Total revenues	$ 13,873,000	$ 17,094,000	$ 23,125,000
Mack-Cali Realty LP [Member] | Parking Income [Member]
REVENUES
Total revenues	21,857,000	21,907,000	20,050,000
Mack-Cali Realty LP [Member] | Hotel Income [Member]
REVENUES
Total revenues	9,841,000
Mack-Cali Realty LP [Member] | Other Income [Member]
REVENUES
Total revenues	$ 9,222,000	$ 8,930,000	$ 12,220,000