Real Estate (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Allocation of the purchase price for One Beach Street
Total assets	$ 1,713,448	$ 1,709,281
Accounts payable and accrued expenses	27,317	25,476
Security deposits payable	4,874	4,790
Other liabilities and deferred credits	54,316	55,808
Total liabilities	1,051,045	1,029,553
Beach Street [Member]
Allocation of the purchase price for One Beach Street
Land	15,332
Building	16,764
Land improvements	30
Tenant improvements	1,223
Total real estate	33,349
Lease intangibles	4,141
Prepaid expenses and other assets	1
Total assets	37,491
Accounts payable and accrued expenses	94
Security deposits payable	75
Lease intangibles	1,382
Other liabilities and deferred credits	22
Total liabilities	$ 1,573