Significant Acquisitions and Dispositions (Summary of Allocation of Fair Value of Amounts Recognized) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Real estate assets	$ 94,783,000	$ 26,276,000
Lease-related intangible assets	8,068,000	2,001,000
Investments in and advances to unconsolidated companies	197,807,000	268,390,000
Gain on dissolution of unconsolidated company	30,697,000	0	$ 0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	102,851,000	28,277,000
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain	7,272,000	$ 0	$ 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, 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, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	137,206,000
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 company	$ 30,697,000