Supplemental Disclosure to Statements of Cash Flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Continuing Operations [Member]
Other Significant Noncash Transactions [Line Items]
Write off of fully depreciated property and deferred costs	$ 18,507	$ 17,672
Write Off Of Depreciated Property And Deferred Costs Due To Sale	20,273	13,127
Change in accrued development capital expenditures	9,636	17,744
Unrealized gain (loss) on cash flow hedge, non cash transaction	493	366
Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount	727	877
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	479	8,937
Write Off Of Depreciated Property And Deferred Costs Due To Sale	99,072	0
Change in accrued development capital expenditures	$ (1,903)	$ 511