Real Estate Investments (Details) - Operating Results Included in the Company's Historical Consolidated Statement of Operations for Properties Acquired During the Reported Periods - USD ($) $ 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
Statement of operations:
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 attributable to Retail Opportunity Investments Corp.	$ 10,849	$ 9,149	$ 8,309	$ 10,170	$ 9,621	$ 7,402	$ 7,704	$ 8,027	38,477	32,754	$ 23,864
Attributable to Acquired Properties During the Reporting Periods
Statement of operations:
Revenues									13,500	15,230
Net income attributable to Retail Opportunity Investments Corp.									$ 2,948	$ 2,513