Summary of Significant Accounting Policies - Properties in Development (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2015
Real Estate and Accumulated Depreciation, Costs Capitalized Subsequent to Acquisition, Carrying Costs	$ 485,025,000
Other Cost and Expense, Operating	1,700,000	$ 2,300,000	$ 528,000
Impairment Losses Related to Real Estate Partnerships	(1,300,000)	(1,300,000)
Deferred Costs, Leasing, Net	66,367,000	60,889,000
Deferred Finance Costs, Net	13,252,000	10,613,000
Deferred costs, less accumulated amortization of $73,231 and $69,224 at December 31, 2013 and 2012, respectively	79,619,000	71,502,000
Refundable deposits - development
Property, Plant and Equipment [Line Items]
Real Estate and Accumulated Depreciation, Costs Capitalized Subsequent to Acquisition, Carrying Costs	$ 1,300,000	$ 375,000