Investments in and Advances to Other Real Estate Partnerships - Condensed Combined Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Assets:
Net Investment in Real Estate	$ 2,117,671		$ 2,095,208
Total Assets	2,514,246		2,498,779
Liabilities:
Mortgage Loans Payable, Net	518,754		580,215
Partners’ Capital	1,100,510		1,180,722		1,155,151	1,081,992
Total Liabilities and Partners’ Capital	2,514,246		2,498,779
Carrying Value of the Operating Partnership’s Investments in Other Real Estate Partnerships	213,041		196,323
Other Real Estate Partnerships
Assets:
Net Investment in Real Estate	278,720		276,294
Note Receivable	77,242		119,364
Other Assets, Net	26,884		33,234
Total Assets	382,846		428,892
Liabilities:
Mortgage Loans Payable, Net	81,231		97,675
Other Liabilities, Net	10,172		13,795
Partners’ Capital	291,443		317,422
Total Liabilities and Partners’ Capital	382,846		428,892
Operating Partnership’s Share of Equity	290,221		316,188
Basis Differentials (1)	(77,180)	[1]	(119,865)	[1]
Carrying Value of the Operating Partnership’s Investments in Other Real Estate Partnerships	$ 213,041		$ 196,323

[1] This amount represents the aggregate difference between the Operating Partnership’s historical cost basis and the basis reflected at the Other Real Estate Partnerships’ level. Basis differentials relate to the elimination of a note receivable and related accrued interest between a Other Real Estate Partnership and wholly owned subsidiaries of the Operating Partnership.