Common Stock of ROIC (Narrative) (Details)		12 Months Ended
	May 01, 2018 USD ($) agreement $ / shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($)	Jul. 31, 2013 USD ($)
Common Stock and Warrants of ROIC (Details) [Line Items]
Common stock, par value (in usd per share) | $ / shares		$ 0.0001	$ 0.0001
Proceeds from the issuance of common stock		$ 34,162,000	$ 25,703,000	$ 4,481,000
Stock issuance costs		$ 478,000	$ 570,000	$ 1,225,000
Stock repurchase program, authorized amount					$ 50,000,000.0
Sales Agreement
Common Stock and Warrants of ROIC (Details) [Line Items]
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	$ 250,000,000.0
Common stock issued (in shares) | shares		1,861,036	1,251,376
Proceeds from the issuance of common stock		$ 34,200,000	$ 24,200,000
Stock issuance costs		$ 342,000	$ 242,000