Supplemental Disclosure to Statements of Cash Flows (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Continuing Operations [Member]
Other Significant Noncash Transactions [Line Items]
Write off of fully depreciated property and deferred costs	$ 16,486	$ 15,560
Write Off Of Depreciated Property And Deferred Costs Due To Sale	19,564	8,989
Change in accrued development capital expenditures	10,532	11,131
Unrealized gain (loss) on cash flow hedge, non cash transaction	487	275
Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount	240	739
Conversion of Stock, Amount Converted	0	27
Discontinued Operations [Member]
Other Significant Noncash Transactions [Line Items]
Write off of fully depreciated property and deferred costs	9	4,273
Write Off Of Depreciated Property And Deferred Costs Due To Sale	96,936	0
Change in accrued development capital expenditures	$ (1,893)	$ 1,993