Consolidated Statements of Cash Flows Supplemental Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Cash Flow Elements [Abstract]
Document Fiscal Year Focus	2015	2014	2013
Interest paid, net of amounts capitalized	$ 29,337	$ 28,840	$ 21,216
Income taxes paid	2	4	90
Non-Cash Transactions:
Transfer from projects under development to operating properties	121,709	0	25,629
Transfer from operating properties to operating properties and related assets held for sale	7,246	0	24,554
Transfer from operating properties and related liabilities to liabilities of real estate assets held for sale	1,347	0	0
Change in accrued property acquisition, development, and tenant asset expenditures	(2,483)	(531)	1,559
Transfer from other assets to projects under development	0	0	3,062
Transfer from land to projects under development	$ 0	$ 5,185	$ 0