Organization, Basis of Presentation and Summary of Significant Accounting Policies (Details) - Reconciliation Between Basic and Diluted EPS - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income	$ 11,126	$ 19,628	$ 8,346	$ 14,583	$ 11,568	$ 15,647	$ 8,102	$ 11,824	$ 53,683	$ 47,141	$ 42,688
Less income attributable to non-controlling interests									(4,839)	(4,405)	(4,211)
Less earnings allocated to unvested shares, basic									(453)	(401)	(319)
Net income available to common stockholders, basic									48,391	42,335	38,158
Less earnings allocated to unvested shares, diluted									(453)	(401)	(319)
Net income available to common stockholders, diluted									$ 53,230	$ 46,740	$ 42,369
Denominator:
Denominator for basic EPS – weighted average common equivalent shares (in shares)									114,177,528	112,645,490	109,400,123
Denominator for diluted EPS – weighted average common equivalent shares (in shares)									125,741,486	124,558,893	121,743,831
Retail Opportunity Investments Partnership L.P.
Numerator:
Net income	$ 11,126	$ 19,628	$ 8,346	$ 14,583	$ 11,568	$ 15,647	$ 8,102	$ 11,824	$ 53,683	$ 47,141	$ 42,688
Less earnings allocated to unvested shares, basic									(453)	(401)	(319)
Net income available to unitholders, basic and diluted									$ 53,230	$ 46,740	$ 42,369
Denominator:
Denominator for basic EPS – weighted average common equivalent shares (in shares)									125,511,936	124,271,802	121,460,958
Denominator for diluted EPS – weighted average common equivalent shares (in shares)									125,741,486	124,558,893	121,743,831
OP Units
Denominator:
OP Units (in shares)									11,334,408	11,626,312	12,060,835
Performance-based restricted stock awards and LTIP Units
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)									206,100	183,683	153,807
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)									206,100	183,683	153,807
Stock options
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)									23,450	103,408	129,066
Stock options | Retail Opportunity Investments Partnership L.P.
Denominator:
Incremental common shares attributable to dilutive effect of share-based payment arrangements (in shares)									23,450	103,408	129,066