Investment in Consolidated and Unconsolidated Entities - Net Equity Investment and Share of Net Income (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of net equity investment and share of net income or loss
Carrying value of investment	$ 185,096	$ 178,728
IAGM Retail Fund I, LLC
Schedule of net equity investment and share of net income or loss
Ownership %	55.00%
Carrying value of investment	$ 128,778	126,090
Downtown Railyard Venture, LLC
Schedule of net equity investment and share of net income or loss
Ownership %	90.00%
Carrying value of investment	$ 56,429	52,365
Other unconsolidated entities
Schedule of net equity investment and share of net income or loss
Carrying value of investment	$ (111)	$ 273