Mortgage Notes Payable, Credit Facilities and Senior Notes (Narrative) (Details)				12 Months Ended
	May 11, 2017 USD ($)	Dec. 03, 2014 USD ($)	Dec. 09, 2013 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Nov. 10, 2017 USD ($)	Oct. 11, 2017 USD ($) loan	Sep. 08, 2017 USD ($)	Jul. 26, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jul. 26, 2016 USD ($)	Sep. 29, 2015 USD ($)
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Number of loans assumed | loan								2
Asset Acquisition, Recognized Identifiable Assets Acquired And Liabilities Assumed, Long-term Debt				$ 46,034,000
Principal repayments on mortgages				8,848,000	$ 7,816,000	$ 84,308,000
Revolving Credit Facility
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Line of credit facility, maximum borrowing capacity									$ 600,000,000		$ 500,000,000
Credit facility				$ 143,500,000	98,000,000
Line of credit facility, interest rate during period (in percentage)				2.10%
Remaining borrowing capacity				$ 456,500,000
Revolving Credit Facility | Accordion Feature
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Line of credit facility, maximum borrowing capacity				$ 1,200,000,000.0
Loan Agreements
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Line of credit facility, commitment fee (in percentage)				0.20%
Line of credit, fronting fee (in percentage)				0.125%
Eurodollar | Loan Agreements
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Basis Spread on variable rate (in percentage)				1.00%
Federal Funds Rate | Loan Agreements
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Basis Spread on variable rate (in percentage)				0.50%
Term Loan Agreement
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Debt, face amount													$ 300,000,000.0
Additional borrowing capacity													$ 200,000,000
Interest rate during period (in percentage)				2.20%
Term Loan Agreement | Federal Funds Effective Swap Rate
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Basis Spread on variable rate (in percentage)				0.50%
Term Loan Agreement | Eurodollar
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Basis Spread on variable rate (in percentage)				1.10%
Senior Notes Due 2027
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Debt, face amount				$ 250,000,000	0		$ 250,000,000
Interest Rate (in percentage)							4.19%
Interest expense, debt				466,000
Deferred finance costs							$ 1,300,000
Senior Notes Due 2026
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Debt, face amount				200,000,000	200,000,000							$ 200,000,000.0
Interest Rate (in percentage)												3.95%
Interest expense, debt				7,900,000	2,200,000
Deferred finance costs										$ 283,000
Senior Notes Due 2024
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Debt, face amount		$ 250,000,000.0
Debt Instrument, Maturity Date		Dec. 15, 2024
Interest Rate (in percentage)		4.00%
Interest expense, debt				10,000,000	10,000,000
Deferred finance costs		$ 2,200,000
Amortization of debt discount				313,000	300,000
Senior Notes Due 2023
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Debt, face amount			$ 250,000,000.0
Debt Instrument, Maturity Date			Dec. 15, 2023
Interest Rate (in percentage)			5.00%
Interest expense, debt				12,500,000	12,500,000
Deferred finance costs			$ 2,600,000
Amortization of debt discount				$ 382,000	$ 363,000
Fullerton Crossroads
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Asset Acquisition, Recognized Identifiable Assets Acquired And Liabilities Assumed, Long-term Debt								$ 26,000,000
Interest Rate (in percentage)				4.728%
Riverstone Marketplace
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Asset Acquisition, Recognized Identifiable Assets Acquired And Liabilities Assumed, Long-term Debt								$ 18,500,000
Interest Rate (in percentage)				4.96%
Bernardo Heights Plaza
Mortgage Notes Payable, Credit Facilities and Senior Notes [Line Items]
Principal repayments on mortgages	$ 8,100,000
Interest Rate (in percentage)				5.70%