Summary of Significant Accounting Policies (Narrative) (Details)			3 Months Ended		12 Months Ended
	Apr. 01, 2019 USD ($)	Jan. 01, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) property segment	Dec. 31, 2018 USD ($) property	Dec. 31, 2017 USD ($)
Class of Stock [Line Items]
Prior period reclassification adjustment				$ 900,000
Weighted average remaining lease term					9 years
Contingent rental income					$ 900,000	$ 900,000	$ 800,000
Bad debt expense					$ 2,900,000	2,700,000	1,100,000
Lease termination fee income	$ 8,000,000.0
Lease termination fee income, net			$ 7,600,000
Number of real estate properties | property					819
Goodwill					$ 0	1,605,000
Goodwill impairment					$ 1,605,000	0	0
Number of reportable segments | segment					1
Mortgage loans					$ 0	0	17,200,000
Cash and cash equivalents					81,898,000	91,451,000	$ 107,666,000
Cash in excess of FDIC limit					80,000,000.0	$ 89,700,000
Operating lease right-of-use assets					18,959,000
Operating lease liabilities					$ 19,318,000
Accounting Standards Update 2016-02
Class of Stock [Line Items]
Accounts receivable write-offs		$ 100,000
Straight-line rent receivable write-offs		100,000
Operating lease right-of-use assets		19,300,000
Operating lease liabilities		19,300,000
Straight-line rent liability		(300,000)
Prepaid rent		100,000
Above Market and Below Market Leases | Accounting Standards Update 2016-02
Class of Stock [Line Items]
Lease intangibles		$ 1,100,000
Impaired real estate investments held for sale
Class of Stock [Line Items]
Number of real estate properties | property					1	7
Minimum
Class of Stock [Line Items]
Lease-up period					6 months
Maximum
Class of Stock [Line Items]
Lease-up period					24 months
Buildings
Class of Stock [Line Items]
Estimated useful life					40 years
Land Improvements
Class of Stock [Line Items]
Estimated useful life					15 years
Fixtures and Improvements
Class of Stock [Line Items]
Estimated useful life					5 years