Related Party Transactions and Arrangements (Subordinated performance fees) (Details) - Advisors - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Cumulative noncompounded annual return (percent)	8.00%
Subordinated Performance Fees [Member]
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions with related party	$ 0	$ 0	$ 0
Subordinate Performance Fees for Listing
Related Party Transaction [Line Items]
Expense from transactions (percent)	15.00%
Subordinate Performance Fee in Event of Liquidation
Related Party Transaction [Line Items]
Expense from transactions (percent)	15.00%