Common Stock of ROIC (Details Textual)		3 Months Ended		42 Months Ended
	Sep. 19, 2014 USD ($) agreement $ / shares	Mar. 31, 2018 USD ($) $ / shares shares	Mar. 31, 2017 USD ($)	Mar. 31, 2018 USD ($) $ / shares shares	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	$ 0.0001
Proceeds from the sale of common stock		$ 1,508,000	$ 0
Registration expenditures		$ 48,000	$ 256,000
Stock repurchase program, authorized amount						$ 50,000,000.0
Sales Agreement
Class of Stock [Line Items]
Number of sales agreements entered into | agreement	3
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	$ 100,000,000.0
Shares sold during the year (shares) | shares		75,314		2,856,136
Proceeds from the sale of common stock		$ 1,500,000		$ 57,700,000
Registration expenditures		$ 19,000		$ 761,000