Investments in and Advances to Other Real Estate Partnerships - Condensed Combined Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Assets:
Net Investment in Real Estate	$ 2,134,146		$ 2,124,526
Real Estate and Other Assets Held for Sale, Net of Accumulated Depreciation and Amortization of $0 and $0	2,085		6,765
Total Assets	2,515,215		2,503,882
Liabilities:
Mortgage Loans Payable	631,880		656,329
Partners’ Capital	1,217,271		1,155,151
Total Liabilities and Partners’ Capital	2,515,215		2,503,882
Carrying Value of the Operating Partnership's Investments in Other Real Estate Partnerships	189,886		178,104
Other Real Estate Partnerships
Assets:
Net Investment in Real Estate	269,077		264,284
Note Receivable	128,444		142,982
Other Assets, Net	33,047		34,476
Total Assets	430,568		441,742
Liabilities:
Mortgage Loans Payable	98,541		107,287
Other Liabilities, Net	12,577		11,570
Partners’ Capital	319,450		322,885
Total Liabilities and Partners’ Capital	430,568		441,742
Operating Partnership's Share of Equity	318,202		321,663
Basis Differentials (1)	(128,316)	[1]	(143,559)	[1]
Carrying Value of the Operating Partnership's Investments in Other Real Estate Partnerships	$ 189,886		$ 178,104

[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.