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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 72,754	$ 67,966	$ 66,640	$ 65,900	$ 63,070	$ 59,354	$ 58,671	$ 56,094	$ 273,260	$ 237,189	$ 192,699
Net income	12,113	10,127	9,197	11,251	10,652	8,215	8,638	8,925	42,688	36,430	25,092
Net income attributable to ROIC	$ 10,849	$ 9,149	$ 8,309	$ 10,170	$ 9,621	$ 7,402	$ 7,704	$ 8,027	$ 38,477	$ 32,754	$ 23,864
Earnings per share - basic and diluted (in usd per share)	$ 0.10	$ 0.08	$ 0.08	$ 0.09	$ 0.09	$ 0.07	$ 0.08	$ 0.08	$ 0.35	$ 0.31	$ 0.25