Related Party Transactions (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related party transaction
Asset management fees		$ 1,782,000	$ 2,264,000	$ 2,702,000
Advisor
Related party transaction
Acquisition and advisory fees as percentage of purchase, development, construction, or improvement of each asset acquired		1.50%
Acquisition and advisory fees as percentage of funds advanced in respect of loan investment		1.50%
Acquisition and advisory fees incurred		$ 600,000	0	100,000
Reimbursement of acquisition expense		$ 100,000	0	100,000
Percentage of debt financing fee payable under loan or line of credit		0.50%
Debt financing fee		$ 200,000
Monthly asset management fee		0.70%
Asset management fees		$ 1,600,000	2,100,000	2,500,000
Development fee paid to advisor or its affiliates		0	0	0
Administrative services cost incurred and expensed		$ 1,300,000	1,200,000	1,500,000
Due diligence services related to asset dispositions			100,000	100,000
Operating expenses in excess of net income		25.00%
Advisor | Minimum
Related party transaction
Operating expenses in excess of average invested assets		2.00%
Advisor
Related party transaction
Administrative services fee	$ 1.3	$ 1,325,000	1.325	1,500,000
Property management fees as percentage of gross revenues of properties		4.00%
Oversight fee as percentage of gross revenues of property managed		0.50%
Property management fees or oversight fees incurred		$ 200,000	$ 600,000	$ 600,000
Construction management fees, percentage		5.00%
Asset Purchases | Advisor
Related party transaction
Percentage of reimbursement of acquisition expense		0.25%
Development, Construction or Improvement of Assets | Advisor
Related party transaction
Percentage of reimbursement of acquisition expense		0.25%
Funds Advanced for Loan Investment | Advisor
Related party transaction
Percentage of reimbursement of acquisition expense		0.25%