Supplemental Disclosure to Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Continuing Operations [Member]
Other Significant Noncash Transactions [Line Items]
Write off of fully depreciated property and deferred costs	$ 6,903	$ 8,090
Write Off Of Depreciated Property And Deferred Costs Due To Sale	3,045	2,506
Change in accrued development capital expenditures	(153)	5,048
Unrealized gain (loss) on cash flow hedge, non cash transaction	385	313
Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount	185	604
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	6	4,190
Write Off Of Depreciated Property And Deferred Costs Due To Sale	96,936	0
Change in accrued development capital expenditures	$ (1,889)	$ 2,373