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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 75,158	$ 73,904	$ 72,341	$ 74,395	$ 72,754	$ 67,966	$ 66,640	$ 65,900	$ 295,798	$ 273,260	$ 237,189
Net income	11,568	15,647	8,102	11,824	12,113	10,127	9,197	11,251	47,141	42,688	36,430
Net income attributable to ROIC	$ 10,501	$ 14,194	$ 7,339	$ 10,702	$ 10,849	$ 9,149	$ 8,309	$ 10,170	$ 42,736	$ 38,477	$ 32,754
Earnings per share - basic and diluted (in usd per share)	$ 0.09	$ 0.12	$ 0.06	$ 0.09	$ 0.10	$ 0.08	$ 0.08	$ 0.09	$ 0.38	$ 0.35	$ 0.31