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, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net income	$ 6,969			$ 19,628			$ 25,141	$ 42,557
Less income attributable to non-controlling interests	(503)	$ (389)	$ (1,134)	(1,770)	$ (761)	$ (1,333)	(2,026)	(3,864)
Less earnings allocated to unvested shares	0			(113)			(127)	(340)
Net income available for common stockholders, basic	6,466			17,745			22,988	38,353
Less earnings allocated to unvested shares	0			(113)			(127)	(340)
Net income available for common stockholders, diluted	$ 6,969			$ 19,515			$ 25,014	$ 42,217
Denominator:
Denominator for basic EPS – weighted average common equivalent shares (in shares)	117,218,094			113,814,447			116,523,448	113,725,752
Denominator for diluted EPS – weighted average common equivalent shares (in shares)	126,610,056			125,540,828			126,812,467	125,498,336
Retail Opportunity Investments Partnership L.P.
Numerator:
Net income	$ 6,969	$ 5,036	$ 13,136	$ 19,628	$ 8,346	$ 14,583	$ 25,141	$ 42,557
Less earnings allocated to unvested shares	0			(113)			(127)	(340)
Net income available to unitholders, basic and diluted	$ 6,969			$ 19,515			$ 25,014	$ 42,217
Denominator:
Denominator for basic EPS – weighted average common equivalent shares (in shares)	126,374,908			125,136,053			126,565,063	125,116,822
Denominator for diluted EPS – weighted average common equivalent shares (in shares)	126,610,056			125,540,828			126,812,467	125,498,336
OP units
Denominator:
OP units (in shares)	9,156,814			11,321,606			10,041,615	11,391,070
Performance-based restricted stock awards and LTIP Units
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	234,944			324,328			244,453	304,427
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)	234,944			324,328			244,453	304,427
Stock options
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	204			80,447			2,951	77,087
Stock options | Retail Opportunity Investments Partnership L.P.
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	204			80,447			2,951	77,087