Real Estate Properties - Summary of Income Statement Information for Properties Included in Discontinued Operations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statements of Operations:
Rental income									$ 409,071	$ 570,382	$ 691,699
Tenant reimbursements and other income									91,609	144,509	170,158
Total revenues	$ 103,546	$ 114,632	$ 145,367	$ 137,135	$ 138,934	$ 159,208	$ 203,694	$ 213,055	500,680	714,891	861,857
Operating expenses									200,706	324,948	387,982
General and administrative									50,256	57,457	113,155
Total expenses									441,244	593,568	913,741
Operating income (loss)									59,436	121,323	(51,884)
Interest and other income									10,331	5,989	1,561
Interest expense									(84,329)	(107,316)	(143,230)
Income from discontinued operations									$ 0	$ 0	8,389
Discontinued operations, properties sold
Statements of Operations:
Rental income											14,243
Tenant reimbursements and other income											1,900
Total revenues											16,143
Operating expenses											7,138
General and administrative											10
Total expenses											7,148
Operating income (loss)											8,995
Interest and other income											2
Interest expense											(608)
Income from discontinued operations											$ 8,389