Organization, Basis of Presentation and Summary of Significant Accounting Policies (Reconciliation Between Basic and Diluted EPS) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income	$ 19,628			$ 15,647			$ 42,557	$ 35,573
Less income attributable to non-controlling interests	(1,770)	$ (761)	$ (1,333)	(1,453)	$ (763)	$ (1,122)	(3,864)	(3,338)
Less earnings allocated to unvested shares	(113)			(100)			(340)	(301)
Net income available for common stockholders, basic	17,745			14,094			38,353	31,934
Less earnings allocated to unvested shares	(113)			(100)			(340)	(301)
Net income available for common stockholders, diluted	$ 19,515			$ 15,547			$ 42,217	$ 35,272
Denominator:
Denominator for basic EPS – weighted average common equivalent shares (in shares)	113,814,447			112,799,637			113,725,752	112,378,343
Denominator for diluted EPS – weighted average common equivalent shares (in shares)	125,540,828			124,825,546			125,498,336	124,410,038
Retail Opportunity Investments Partnership L.P.
Numerator:
Net income	$ 19,628	$ 8,346	$ 14,583	$ 15,647	$ 8,102	$ 11,824	$ 42,557	$ 35,573
Less earnings allocated to unvested shares	(113)			(100)			(340)	(301)
Net income available to unitholders, basic and diluted	$ 19,515			$ 15,547			$ 42,217	$ 35,272
Denominator:
Denominator for basic EPS – weighted average common equivalent shares (in shares)	125,136,053			124,409,038			125,116,822	124,031,633
Denominator for diluted EPS – weighted average common equivalent shares (in shares)	125,540,828			124,825,546			125,498,336	124,410,038
OP units
Denominator:
OP units (in shares)	11,321,606			11,609,401			11,391,070	11,653,290
Performance-based restricted stock awards and LTIP Units
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	324,328			301,729			304,427	270,325
Performance-based restricted stock awards and LTIP Units | Retail Opportunity Investments Partnership L.P.
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	324,328			301,729			304,427	270,325
Stock options
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	80,447			114,779			77,087	108,080
Stock options | Retail Opportunity Investments Partnership L.P.
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	80,447			114,779			77,087	108,080