Capital of the Operating Partnership (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions				12 Months Ended
		Dec. 12, 2017	Jul. 12, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 11, 2017	Dec. 31, 2014
Capital of the Operating Partnership [Line Items]
Ownership interest (in percentage)				90.50%
Shares outstanding (in shares)				112,347,451	109,301,762
Remaining units outstanding ( in shares)				124,026,442
Proceeds from the issuance of common stock (in shares)			6,555,000
Cash redemption of OP Units (in shares)				157,567
ROIC common stock (in shares)				150,503
Equity redemption of OP Units, cash (in shares)				7,064
OP Units
Capital of the Operating Partnership [Line Items]
Non-controlling interest redemption value (in usd per share)				$ 19.65
Non-controlling interest redemption value				$ 229.5
Common Stock
Capital of the Operating Partnership [Line Items]
Shares outstanding (in shares)				112,347,451	109,301,762	99,531,034		92,991,333
Proceeds from the issuance of common stock (in shares)				212,825	8,757,254	6,064,567
ROIC common stock (in shares)				150,503	755,762	174,959
Retail Opportunity Investments Partnership L.P. | Limited Partner’s Capital
Capital of the Operating Partnership [Line Items]
Limited Partners' Capital Account, Units Outstanding	[1]			11,678,991
Remaining units outstanding ( in shares)	[1]				11,668,061	12,195,603		3,921,314
Cash redemption of OP Units (in shares)	[1]			7,064	2,206,613
ROIC common stock (in shares)	[1]			(2,555,933)	(755,762)	(174,959)
Fullerton Crossroads and Riverstone Marketplace
Capital of the Operating Partnership [Line Items]
LP capital account, units issued (in shares)							2,405,430
Fullerton Crossroads and Riverstone Marketplace | Vancouver, Washington
Capital of the Operating Partnership [Line Items]
LP capital account, units issued (in shares)							2,405,430
Restricted cash		$ 3.8
Proceeds from the issuance of common stock (in shares)		2,584,254

[1] Consists of limited partnership interests held by third parties.