Related Parties (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) property	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) property	Dec. 31, 2013 USD ($) property
Related Party Transaction [Line Items]
Net accounts receivable, related parties	$ 1,400		$ 1,400		$ 1,500
Accounts payable and accrued expenses, related parties	5,400		5,400		6,000
Management fees revenues, related parties	1,100	$ 1,100	3,400	$ 3,500
Total assets	3,895,337		3,895,337		$ 3,814,094
Debt, net	$ 1,897,107		$ 1,897,107
Number of operating properties sold | property			8
Increase in equity			$ 0	11,015
Gain on sale of property			$ 43,917	115,989
Acquisition of noncontrolling interests				0
Disposition of noncontrolling interests				$ (144,263)
Hines [Member]
Related Party Transaction [Line Items]
Ownership percentage in joint ventures					30.00%
Number of real estate properties | property					5	13
Total assets						$ 172,900
Debt, net						$ 11,100
Number of operating properties sold | property					8
Increase in equity					$ 11,000
Gain on sale of property					23,300
Acquisition of noncontrolling interests					(11,000)
Disposition of noncontrolling interests					$ 144,300