Related Party Transactions and Arrangements - Investment in the Cole REITs Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Aggregate equity investments	$ 42,784	$ 46,077
Net loss	(2,726)	415	$ (2,361)
Cole REITs [Member]
Related Party Transaction [Line Items]
Aggregate equity investments	3,264
Net loss	500	1,300	$ (100)
Cole REITs [Member]
Related Party Transaction [Line Items]
Aggregate equity investments	$ 3,300	$ 4,700