Related Party Transactions and Arrangements (Advisor and its Affiliates) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Related Party Transaction [Line Items]
Fees paid to related parties	$ 3,767,000	$ 3,328,000
Advisor
Related Party Transaction [Line Items]
Cost of assets maximum	$ 3,000,000,000
Asset management fees earned above	0.40%
Average Invested Assets | Advisor
Related Party Transaction [Line Items]
Asset management fees as a percentage of benchmark	0.50%
Cost of assets maximum	$ 3,000,000,000
Gross Revenue, Multi-tenant Properties | Advisor
Related Party Transaction [Line Items]
Property management fees as a percentage of benchmark	4.00%
Maximum | Average Invested Assets | Advisor
Related Party Transaction [Line Items]
Operating expenses as a percentage of benchmark	2.00%
Maximum | Gross Revenue, Managed Properties | Advisor
Related Party Transaction [Line Items]
Oversight fees as a percentage of benchmark	1.00%
Maximum | Net Income, Excluding Additions to Non-cash Reserves and Gains on Sales of Assets | Advisor
Related Party Transaction [Line Items]
Operating expenses as a percentage of benchmark	25.00%
Maximum | Contract Sales Price | Advisor
Related Party Transaction [Line Items]
Real estate commission earned by related party	2.00%
Reimbursement of Costs and Expenses | Advisor
Related Party Transaction [Line Items]
Fees paid to related parties	$ 700,000	0
Brokerage Commission Fees | Maximum | Contract Sales Price | Advisor
Related Party Transaction [Line Items]
Real estate commission earned by related party	50.00%
Real Estate Commissions | Maximum | Contract Sales Price | Advisor
Related Party Transaction [Line Items]
Real estate commission earned by related party	6.00%
Property Disposition Fees | Advisor
Related Party Transaction [Line Items]
Fees paid to related parties	$ 200,000	$ 0