Common Stock of ROIC (Details Textual)		9 Months Ended		17 Months Ended
	May 01, 2018 USD ($) agreement $ / shares	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2018 $ / 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		$ 16,351,000	$ 25,703,000
Registration expenditures		$ 272,000	$ 376,000
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	$ 250,000,000.0
Shares sold during the period (in shares) | shares		888,865		2,140,241
Proceeds from the sale of common stock		$ 16,300,000		$ 40,500,000
Registration expenditures		$ 163,000		$ 405,000