Capital of the Operating Partnership (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Capital of the Operating Partnership [Line Items]
Partnership units ( in shares)		127,547,106
Shares outstanding (in shares)		116,496,016	113,992,837
Notices of redemptions received		425,951
Cash redemption of OP Units (in shares)		282,761
Cash redemption for non-controlling interests		$ 5,043	$ 3,713	$ 150
Equity Redemption of OP Units (in shares)		143,190
Common Stock
Capital of the Operating Partnership [Line Items]
Shares outstanding (in shares)		116,496,016	113,992,837	112,347,451	109,301,762
Equity Redemption of OP Units (in shares)		143,190		2,555,933
OP Units
Capital of the Operating Partnership [Line Items]
Non-controlling interest redemption value		$ 191,500
Non-controlling interest redemption value (in usd per share)		$ 17.33
Retail Opportunity Investments Partnership L.P.
Capital of the Operating Partnership [Line Items]
Cash redemption for non-controlling interests		$ 5,043	$ 3,713	$ 150
Limited Partner’s Capital | Retail Opportunity Investments Partnership L.P.
Capital of the Operating Partnership [Line Items]
Partnership units ( in shares)	[1]	11,051,090	11,477,041	11,678,991	11,668,061
Cash redemption of OP Units (in shares)	[1]	282,761	201,950	7,064
Cash redemption for non-controlling interests	[1]	$ 5,043	$ 3,713	$ 150
Equity Redemption of OP Units (in shares)	[1]	(143,190)		(2,555,933)
Retail Opportunity Investments Partnership L.P.
Capital of the Operating Partnership [Line Items]
ROIC ownership percentage in ROIP LP		91.30%

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