Real Estate Properties (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statements of Operations:
Rental income	$ 172,040	$ 211,300
Tenant reimbursements and other income	45,220	51,312
Total revenues	217,260	262,612
Operating expenses	101,731	104,130
Depreciation and amortization	51,649	62,570
General and administrative	24,848	16,663
Total expenses	173,472	183,991
Operating income	43,788	78,621
Interest and other income	384	455
Interest expense	(37,935)	(51,896)
Income (loss) from discontinued operations	4,011	(6)
Discontinued operations, properties sold or held for sale
Statements of Operations:
Rental income	7,274	15,512
Tenant reimbursements and other income	522	1,731
Total revenues	7,796	17,243
Operating expenses	3,479	11,564
Depreciation and amortization		3,953
General and administrative	3	1,287
Total expenses	3,482	16,804
Operating income	4,314	439
Interest and other income		3
Interest expense	(303)	(448)
Income (loss) from discontinued operations	$ 4,011	$ (6)