Discontinued Operations Discontinued Operations (Details) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Revenue:
Rents	$ 116,334,000		$ 109,713,000	$ 231,201,000	$ 218,704,000
Tenant reimbursements	19,565,000		18,229,000	39,916,000	36,885,000
Termination fees	410,000		101,000	906,000	1,591,000
Other Real Estate Revenue	1,457,000		888,000	2,330,000	2,399,000
Total revenue	140,919,000		131,803,000	280,742,000	265,593,000
Expenses:
Property operating expenses	39,490,000		36,363,000	78,908,000	74,223,000
Real estate taxes	14,215,000		13,508,000	28,552,000	26,977,000
Depreciation and amortization	49,300,000		47,476,000	98,846,000	95,350,000
Total operating expenses	111,703,000		104,690,000	222,980,000	211,193,000
Interest income	122,000		1,838,000	180,000	2,320,000
Income from discontinued operations before gain on sale of interests in real estate	8,000		2,535,000	780,000	5,275,000
Net gain on disposition of discontinued operations	(2,260,000)	[1]	10,177,000	3,044,000	24,845,000
Income from discontinued operations	(2,252,000)		12,712,000	3,824,000	30,120,000
Discontinued Operations, Disposal Closing Costs	1,100,000	[1]
Discontinued Operations [Member]
Revenue:
Rents	626,000		7,322,000	4,129,000	16,680,000
Tenant reimbursements	2,000		719,000	331,000	1,486,000
Termination fees			0		7,000
Other Real Estate Revenue	9,000		164,000	123,000	188,000
Total revenue	637,000		8,205,000	4,583,000	18,361,000
Expenses:
Property operating expenses	274,000		2,137,000	1,586,000	4,841,000
Real estate taxes	79,000		843,000	504,000	1,977,000
Depreciation and amortization	278,000		2,695,000	1,715,000	6,274,000
Total operating expenses	631,000		5,675,000	3,805,000	13,092,000
Interest income	2,000		5,000	2,000	6,000
Income from discontinued operations before gain on sale of interests in real estate	8,000		2,535,000	780,000	5,275,000
Net gain on disposition of discontinued operations			10,177,000	3,044,000	24,845,000
Income from discontinued operations	$ (2,252,000)		$ 12,712,000	$ 3,824,000	$ 30,120,000

[1] The loss of $(2.3) million for the second quarter of 2013 includes $1.1 million of closing costs incurred to sell the properties.