Mack-Cali Realty Corporation Stockholders' Equity And Mack-Cali Realty, L.P.'s Partners' Capital (Share/Unit Repurchase Program And Dividend Reinvestment And Stock Purchase Plan) (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2012
Stockolders Equity [Line Items]
Date share repurchase program was initiated	September 2012
Capacity of share repurchase program	$ 150,000,000
Shares purchased and retired	394,625
Aggregate cost of stock repurchased	$ 11,000,000
Capacity available for additional repurchase of outstanding common stock	$ 139,000,000
Proceeds from sale of common units		$ 11,000,000
Dividend Reinvestment And Stock Purchase Plan [Member]
Stockolders Equity [Line Items]
Common stock reserved for future issuance	5,500,000
Monthly cash investment without restriction, maximum	$ 5,000