Real Estate Investments - Summary of Properties Classified as Held for Sale Included in Continuing Operations (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
ASSETS HELD FOR SALE
Operating properties	$ 16,916
Accumulated depreciation	(4,524)
Operating real estate investments, net	12,392
Construction-in-progress	212
Total real estate investments, net	12,604
Other assets	0
Total assets held for sale, net	12,604	$ 584,365
LIABILITIES HELD FOR SALE
Other liabilities	49
Total liabilities held for sale	49	$ 2,151
Held for Sale Properties Included in Continuing Operations [Member] | 620, 640 and 660 Allendale Road [Member]
ASSETS HELD FOR SALE
Operating properties	12,550
Accumulated depreciation	(4,520)
Operating real estate investments, net	8,030
Construction-in-progress	212
Total real estate investments, net	8,242
Other assets	0
Total assets held for sale, net	8,242
LIABILITIES HELD FOR SALE
Other liabilities	49
Total liabilities held for sale	49
Held for Sale Properties Included in Continuing Operations [Member] | Oakland Lot B [Member]
ASSETS HELD FOR SALE
Operating properties	4,366
Accumulated depreciation	(4)
Operating real estate investments, net	4,362
Construction-in-progress	0
Total real estate investments, net	4,362
Other assets	0
Total assets held for sale, net	4,362
LIABILITIES HELD FOR SALE
Other liabilities	0
Total liabilities held for sale	$ 0