Discontinued Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Revenue:
Rents	$ 121,671	$ 114,608
Other Real Estate Revenue	630	873
Tenant reimbursements	23,460	20,341
Total revenue	152,114	139,554
Expenses:
Property operating expenses	46,801	39,349
Real estate taxes	13,457	14,295
Depreciation and amortization	52,570	49,476
Total operating expenses	122,725	111,096
Interest income	385	58
Income from discontinued operations before gain on sale of interests in real estate	(8)	860
Net gain on disposition of discontinued operations	0	5,304
Income (Loss) from discontinued operations	(8)	6,164
Discontinued Operations [Member]
Revenue:
Rents		3,763
Termination fees		0
Other Real Estate Revenue		114
Tenant reimbursements		338
Total revenue		4,215
Expenses:
Property operating expenses		1,382
Real estate taxes		466
Depreciation and amortization		1,507
Total operating expenses		3,355
Interest income		0
Income from discontinued operations before gain on sale of interests in real estate		860
Net gain on disposition of discontinued operations		5,304
Income (Loss) from discontinued operations		$ 6,164