Summary of Significant Accounting Policies - Condensed Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Assets:
Net Investment in Real Estate	$ 2,448,098	$ 2,396,391
Total Assets	2,706,680	2,581,995
LIABILITIES AND EQUITY
Mortgage Loans Payable, Net	590,912	599,985
Total Liabilities and Equity	2,706,680	2,581,995
Other Real Estate Partnership
Assets:
Net Investment in Real Estate	299,533	278,720
Other Assets, Net	20,433	21,078
Total Assets	319,966	299,798
LIABILITIES AND EQUITY
Mortgage Loans Payable, Net	80,023	81,231
Other Liabilities, Net	26,171	10,656
Partners’ Capital	213,772	207,911
Total Liabilities and Equity	$ 319,966	$ 299,798