Financing Activity - Credit Agreements (Details)		12 Months Ended
	May 24, 2018 USD ($)	Dec. 31, 2019 USD ($) Agreement qtr Occasion	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Outstanding line of credit		$ 255,000,000	$ 65,000,000
Debt instrument, covenant compliance		As of December 31, 2019, we were in compliance with all such financial covenants. We anticipate not meeting certain financial covenants applicable under the credit agreements during 2020. See Going Concern Considerations section in Note 1.
Unsecured Debt
Debt Instrument [Line Items]
Debt issuance costs, line of credit arrangements		$ 2,000,000.0
Term Loans
Debt Instrument [Line Items]
Outstanding borrowings		550,000,000.0
2018 Revolving Facility
Debt Instrument [Line Items]
Outstanding line of credit		$ 255,000,000.0
Credit Agreements
Debt Instrument [Line Items]
Number of credit agreements | Agreement		2
Deferred financing amortization	$ 400,000
Credit Agreements | Covenant Term One
Debt Instrument [Line Items]
Covenant compliance, Minimum Tangible Net Worth		$ 1,463,200,000
Covenant compliance, percent of net proceeds of all equity issuances		75.00%
Credit Agreements | Covenant Term Two
Debt Instrument [Line Items]
Total liabilities to gross asset value, ratio		0.60
Covenant compliance, number of consecutive quarters total liabilities to gross asset value ratio exceeding threshold | qtr		2
Covenant compliance, number of occasions total liabilities to gross asset value ratio exceeding threshold | Occasion		2
Credit Agreements | Covenant Term Two | Maximum
Debt Instrument [Line Items]
Total liabilities to gross asset value, ratio		0.625
Credit Agreements | Covenant Term Three
Debt Instrument [Line Items]
Covenant compliance, ratio of adjusted EBITDA to fixed charges, minimum		1.50
Credit Agreements | Covenant Term Four, Through June 30, 2020
Debt Instrument [Line Items]
Covenant compliance, minimum unencumbered debt yield		0.110
Credit Agreements | Covenant Term Four, After June 30, 2020 Through June 30, 2021
Debt Instrument [Line Items]
Covenant compliance, minimum unencumbered debt yield		0.1125
Credit Agreements | Covenant Term Four, After June 30, 2021
Debt Instrument [Line Items]
Covenant compliance, minimum unencumbered debt yield		0.1150
Credit Agreements | Covenant Term Five
Debt Instrument [Line Items]
Covenant compliance, minimum unencumbered NOI to unsecured interest expense, ratio		1.75
Credit Agreements | Covenant Term Six
Debt Instrument [Line Items]
Covenant compliance, secured indebtedness to gross asset value, maximum ratio		0.60
Credit Agreements | Covenant Term Seven
Debt Instrument [Line Items]
Covenant compliance, maximum distribution percent of funds from operations		95.00%
Covenant compliance, maximum distribution percent of REIT taxable income		110.00%
Credit Agreements | Property With Average Sales Of More Than $500 Per Square Foot
Debt Instrument [Line Items]
Covenant compliance, capitalization rate		6.50%
Credit Agreements | Property Other Than With Average Sales Of $500 Per Square Foot
Debt Instrument [Line Items]
Covenant compliance, capitalization rate		7.50%
Credit Agreements | Term Loans
Debt Instrument [Line Items]
Outstanding borrowings		$ 550,000,000.0
Deferred financing amortization		760,000	763,000	$ 759,000
Credit Agreements | 2018 Revolving Facility
Debt Instrument [Line Items]
Outstanding line of credit		255,000,000.0
Remaining borrowing capacity		30,100,000
Maximum borrowing capacity	$ 400,000,000
Credit facility maturity date	2022-05
Deferred financing amortization		$ 1,097,000	$ 1,052,000	$ 796,000
Facility fee percentage		0.30%
Credit Agreements | Senior Unsecured Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 700,000.0
Credit Agreements | 2013 Revolving Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	400,000,000
Credit Agreements | 2018 Term Loan Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 300,000,000
Credit facility maturity date	2023-05
Credit Agreements | 2014 5-Year Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 150,000,000
Credit Agreements | 2015 5-Year Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 150,000,000
Credit Agreements | 2014 Seven Year Term Loan
Debt Instrument [Line Items]
Outstanding line of credit		$ 250,000,000.0
Credit facility maturity date		2021-12