Common Stock of ROIC (Details Textual)			9 Months Ended		24 Months Ended
	Jul. 12, 2016 USD ($) shares	Sep. 19, 2014 USD ($) agreement $ / shares	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) $ / shares shares	Dec. 31, 2015 $ / shares	Jul. 31, 2013 USD ($)
Class of Stock [Line Items]
Proceeds from the sale of common stock	$ 133,000,000		$ 184,881,000	$ 101,293,000
Common stock, par value (in dollars per share) | $ / shares			$ 0.0001		$ 0.0001	$ 0.0001
Registration expenditures			$ 6,983,000	$ 4,286,000
Stock repurchase program, authorized amount							$ 50,000,000.0
Sales Agreement
Class of Stock [Line Items]
Shares sold during the year (shares) | shares			2,202,254		2,746,821
Proceeds from the sale of common stock			$ 45,600,000		$ 55,500,000
Number of sales agreements entered into | agreement		4
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
Registration expenditures			584,000		733,000
Revolving Credit Facility
Class of Stock [Line Items]
Maximum borrowing capacity			$ 500,000,000.0		$ 500,000,000.0
Common Stock | Public Offering [Member]
Class of Stock [Line Items]
Shares sold during the year (shares) | shares	6,555,000