Organization, Basis of Presentation and Summary of Significant Accounting Policies (Reconciliation Between Basic and Diluted EPS) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net income	$ 5,036		$ 8,346		$ 18,172	$ 22,929
Less income attributable to non-controlling interests	(389)	$ (1,134)	(761)	$ (1,333)	(1,523)	(2,094)
Less earnings allocated to unvested shares	0		(113)		(127)	(227)
Net income available for common stockholders, basic	4,647		7,472		16,522	20,608
Less earnings allocated to unvested shares	0		(113)		(127)	(227)
Net income available for common stockholders, diluted	$ 5,036		$ 8,233		$ 18,045	$ 22,702
Denominator:
Denominator for basic EPS – weighted average common equivalent shares (in shares)	116,374,154		113,680,670		116,172,307	113,680,670
Denominator for diluted EPS – weighted average common equivalent shares (in shares)	126,548,035		125,458,232		126,878,856	125,458,113
Retail Opportunity Investments Partnership L.P.
Numerator:
Net income	$ 5,036	$ 13,136	$ 8,346	$ 14,583	$ 18,172	$ 22,929
Less earnings allocated to unvested shares	0		(113)		(127)	(227)
Net income available to unitholders, basic and diluted	$ 5,036		$ 8,233		$ 18,045	$ 22,702
Denominator:
Denominator for basic EPS – weighted average common equivalent shares (in shares)	126,374,908		125,087,711		126,661,184	125,107,048
Denominator for diluted EPS – weighted average common equivalent shares (in shares)	126,548,035		125,458,232		126,878,856	125,458,113
OP units
Denominator:
OP units (in shares)	10,000,754		11,407,041		10,488,877	11,426,378
Performance-based restricted stock awards and LTIP Units
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	173,127		273,996		213,320	255,574
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)	173,127		273,996		213,320	255,574
Stock options
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	0		96,525		4,352	95,491
Stock options | Retail Opportunity Investments Partnership L.P.
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)	0		96,525		4,352	95,491