Real Estate Investments (Development Activities) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($) development_project	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Number of development projects completed | development_project	27
Aggregate cost to date	$ 47,600
Number of remaining projects to be completed | development_project	10
Estimated completion period for remaining projects	12 months
Number of development projects placed into service | development_project	2
Aggregate cost of projects placed in service	$ 55,800
Number of other build-to-suit, redevelopment and expansion projects | development_project	4
Investment to date	$ 37,356	$ 77,450
Total commitment	4,100
Land and Construction in Progress [Member]
Business Acquisition [Line Items]
Tenant Improvements	$ 16,700
2015 Acquisitions [Member]
Business Acquisition [Line Items]
Development projects in progress | development_project	14
Investment to date	$ 17,666
Estimated cost to complete	7,447
Total Investment	$ 25,113