Common Stock of ROIC (Narrative) (Details)				12 Months Ended
	May 01, 2018 USD ($) agreement $ / shares	Dec. 12, 2017 $ / shares shares	Jul. 12, 2016 USD ($) shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)	Oct. 11, 2017 shares	Jul. 31, 2013 USD ($)
Common Stock and Warrants of ROIC (Details) [Line Items]
Common stock issued (in shares) | shares			6,555,000
Proceeds from the issuance of common stock			$ 133,000,000	$ 25,703,000	$ 4,481,000	$ 184,881,000
Common stock, par value (in usd per share) | $ / shares				$ 0.0001	$ 0.0001
Stock issuance costs				$ 570,000	$ 1,225,000	$ 7,097,000
Stock repurchase program, authorized amount								$ 50,000,000.0
Sales Agreement
Common Stock and Warrants of ROIC (Details) [Line Items]
Common stock issued (in shares) | shares				1,251,376
Proceeds from the issuance of common stock				$ 24,200,000
Number of sales agreements | agreement	5
Common stock, par value (in usd per share) | $ / shares	$ 0.0001
Common shares that may be sold under a sales agreement aggregate offering price, maximum	$ 250,000,000.00
Stock issuance costs				$ 242,000
Prior Sales Agreements [Member]
Common Stock and Warrants of ROIC (Details) [Line Items]
Common stock issued (in shares) | shares				75,314	34,001
Proceeds from the issuance of common stock				$ 1,500,000	$ 681,000
Stock issuance costs				$ 19,000	9,000
Fullerton Crossroads and Riverstone Marketplace
Common Stock and Warrants of ROIC (Details) [Line Items]
LP capital account, units issued (in shares) | shares							2,405,430
Common stock issued (in shares) | shares		2,584,254
Share price (usd per share) | $ / shares		$ 21.25
Restricted cash					$ 3,800,000