Common Stock of ROIC (Details Textual)		6 Months Ended
	May 01, 2018 USD ($) agreement $ / shares	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2017 USD ($)	Dec. 31, 2017 $ / shares	Jul. 31, 2013 USD ($)
Class of Stock [Line Items]
Common stock, par value (in dollars per share) | $ / shares		$ 0.0001		$ 0.0001
Proceeds from the sale of common stock		$ 1,508,000	$ 0
Registration expenditures		$ 118,000	$ 348,000
Stock repurchase program, authorized amount					$ 50,000,000.0
Sales Agreement
Class of Stock [Line Items]
Number of sales agreements entered into | agreement	5
Common stock, par value (in dollars per share) | $ / shares	$ 0.0001
Common shares that may be sold under a sales agreement, aggregate offering price, maximum	$ 250,000,000.00
Prior Sales Agreements
Class of Stock [Line Items]
Shares sold during the year (shares) | shares		75,314
Proceeds from the sale of common stock		$ 1,500,000
Registration expenditures		$ 19,000