Investment in Unconsolidated Joint Ventures (Wildwood Associates) (Details) $ in Thousands	Dec. 31, 2017 USD ($) a	Dec. 31, 2016 USD ($)
Schedule of Equity Method Investments [Line Items]
Company's investment balance	$ 78,940	$ 156,388
Wildwood Associates
Schedule of Equity Method Investments [Line Items]
Ownership percentage of partner in joint venture	50.00%
Company's investment balance	$ (1,151)	$ (1,143)
Cash balance of joint venture	$ 74
Wildwood Associates | IBM
Schedule of Equity Method Investments [Line Items]
Ownership percentage of partner in joint venture	50.00%
Acres of land available for development or sale (acres) | a	22