Significant Acquisitions and Dispositions (Summary of Allocation of Fair Value of Amounts Recognized) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real estate assets	$ 945,844,000	$ 94,783,000
Lease-related intangible assets	46,807,000	8,068,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	992,651,000	102,851,000
Below Market Lease, Gross	1,483,000
Business Combination, Consideration Transferred		(131,300,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	991,168,000
Investments in and advances to unconsolidated companies	(126,487,000)	(197,807,000)
Gain on dissolution of unconsolidated joint venture	0	30,697,000	$ 0
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain	$ 0	7,272,000	$ 0
Duke/Quantico LLC [Member]
Real estate assets		120,608,000
Lease-related intangible assets		16,724,000
Net working capital liabilities		(126,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		137,206,000
Business Combination, Consideration Transferred		(131,250,000)
Business Combination, Step Acquisition, Equity Interest in Acquiree, Fair Value		5,956,000
Investments in and advances to unconsolidated companies		0
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain		5,956,000
Duke Realty Limited Partnership [Member]
Real estate assets		63,000,000
Proceeds from Divestiture of Businesses and Interests in Affiliates		2,760,000
Equity Method Investments		(35,063,000)
Gain on dissolution of unconsolidated joint venture		$ 30,697,000