Quarterly Results of Operations (Unaudited) (Details) - Quarterly Results of Operations for ROIC - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 73,619	$ 72,438	$ 72,930	$ 76,053	$ 75,158	$ 73,904	$ 72,341	$ 74,395	$ 295,040	$ 295,798	$ 273,260
Net income	11,126	19,628	8,346	14,583	11,568	15,647	8,102	11,824	53,683	47,141	42,688
Net income attributable to ROIC	$ 10,151	$ 17,858	$ 7,585	$ 13,250	$ 10,501	$ 14,194	$ 7,339	$ 10,702	$ 48,844	$ 42,736	$ 38,477
Earnings per share - basic and diluted (in usd per share)	$ 0.09	$ 0.16	$ 0.07	$ 0.12	$ 0.09	$ 0.12	$ 0.06	$ 0.09	$ 0.42	$ 0.38	$ 0.35