Variable Interest Entities - Summarized Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets:
Net Investment in Real Estate	$ 2,814,725	$ 2,705,826
Total Assets	3,125,327	2,941,062
Liabilities and Partners' Capital:
Mortgage Loans Payable, Net	298,188	450,056
Total Liabilities and Equity/Partners' Capital	3,125,327	2,941,062
Other Real Estate Partnerships
Assets:
Net Investment in Real Estate	265,089	270,708
Other Assets, Net	26,408	23,530
Total Assets	291,497	294,238
Liabilities and Partners' Capital:
Mortgage Loans Payable, Net	20,611	61,256
Other Liabilities, Net	8,296	9,283
Partners' Capital	262,590	223,699
Total Liabilities and Equity/Partners' Capital	$ 291,497	$ 294,238