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, 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
Numerator:
Net income	$ 12,113	$ 10,127	$ 9,197	$ 11,251	$ 10,652	$ 8,215	$ 8,638	$ 8,925	$ 42,688	$ 36,430	$ 25,092
Less income attributable to non-controlling interests									(4,211)	(3,676)	(1,228)
Less earnings allocated to unvested shares, basic									(319)	(270)	(229)
Less earnings allocated to unvested shares, diluted									(319)	(270)	(229)
Net income available to common stockholders, basic									38,158	32,484	23,635
Net income available to common stockholders, diluted									$ 42,369	$ 36,160	$ 24,863
Denominator:
Denominator for basic EPS – weighted average common equivalent shares (in shares)									109,400,123	104,072,222	95,651,780
OP Units (in shares)									12,060,835	11,747,509	4,086,724
Denominator for diluted EPS – weighted average common equivalent shares (in shares)									121,743,831	116,039,940	100,017,781
Retail Opportunity Investments Partnership L.P.
Numerator:
Net income	$ 12,113	$ 10,127	$ 9,197	$ 11,251	$ 10,652	$ 8,215	$ 8,638	$ 8,925	$ 42,688	$ 36,430	$ 25,092
Less earnings allocated to unvested shares, basic									(319)	(270)	(229)
Net income available to unitholders, basic and diluted									$ 42,369	$ 36,160	$ 24,863
Denominator:
Denominator for basic EPS – weighted average common equivalent shares (in shares)									121,460,958	115,819,731	99,738,504
Denominator for diluted EPS – weighted average common equivalent shares (in shares)									121,743,831	116,039,940	100,017,781
Restricted stock awards – performance-based
Denominator:
Restricted units and stock options (in shares)									153,807	86,996	174,198
Restricted stock awards – performance-based | Retail Opportunity Investments Partnership L.P.
Denominator:
Restricted units and stock options (in shares)									153,807	86,996	174,198
Stock options
Denominator:
Restricted units and stock options (in shares)									129,066	133,213	105,079
Stock options | Retail Opportunity Investments Partnership L.P.
Denominator:
Restricted units and stock options (in shares)									129,066	133,213	105,079