Financing Activity - Credit Agreements (Details)				9 Months Ended
	Oct. 16, 2020 USD ($)	Jul. 27, 2020	Mar. 30, 2020 USD ($) qtr Occasion	Sep. 30, 2020 USD ($) Agreement	Nov. 01, 2020 USD ($)	Aug. 11, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)
Debt Instrument [Line Items]
Maximum borrowing capacity							$ 375,000,000.0
Outstanding line of credit				$ 375,000,000				$ 255,000,000
Unrestricted cash				36,373,000				$ 12,211,000	$ 11,709,000
Unsecured Debt
Debt Instrument [Line Items]
Debt issuance costs, line of credit arrangements				(1,500,000)
2018 Revolving Facility
Debt Instrument [Line Items]
Outstanding line of credit				$ 375,000,000.0
Bridge Facility
Debt Instrument [Line Items]
Debt instrument, maturity date				Oct. 31, 2020
Outstanding line of credit				$ 22,500,000
Prepayment percentage of net cash proceeds from certain capital events				100.00%
Debt instrument, payment terms				7 years
Bridge Facility | Maximum
Debt Instrument [Line Items]
Unrestricted cash liquidity				$ 12,500,000
Credit Agreements
Debt Instrument [Line Items]
Number of credit agreements | Agreement				3
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, Prior to and Including September 30, 2020
Debt Instrument [Line Items]
Total liabilities to gross asset value, ratio			0.65
Credit Agreements | Covenant Term Two, Thereafter
Debt Instrument [Line Items]
Total liabilities to gross asset value, ratio			0.60
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, Thereafter
Debt Instrument [Line Items]
Covenant compliance, ratio of adjusted EBITDA to fixed charges, minimum			1.50
Credit Agreements | Covenant Term Three, on or Before September 30, 2020
Debt Instrument [Line Items]
Covenant compliance, ratio of adjusted EBITDA to fixed charges, minimum			1.40
Credit Agreements | Covenant Term Four, Through September 30, 2020
Debt Instrument [Line Items]
Covenant compliance, minimum unencumbered debt yield			0.100
Credit Agreements | Covenant Term Four, After September 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 Net Operating Income 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 | Covenant Term, During Suspension Period
Debt Instrument [Line Items]
Unrestricted cash liquidity			$ 8,500,000
Credit Agreements | Covenant Term, End of Suspension Period and through September 30, 2020
Debt Instrument [Line Items]
Unrestricted cash liquidity			25,000,000.0
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 | Subsequent Event
Debt Instrument [Line Items]
Outstanding line of credit					$ 896,500,000
Credit Agreements | 2018 Revolving Facility
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 375,000,000.0			$ 375,000,000.0
Reduced aggregate revolving commitments			$ 25,000,000.0
Outstanding line of credit				375,000,000.0
Facility fee percentage		0.35%
Credit Agreements | 2018 Term Loan Facility
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 300,000,000.0
Prepayment percentage of net cash proceeds from certain capital events				54.55%
Applicable percentage repayment of outstanding amount provided net proceeds from capital exceeds one fifty million				50.00%
Remaining percentage repayment of outstanding amount provided net proceeds from capital exceeds one fifty million				50.00%
Debt instrument, payment terms				7 years
Remaining percentage of net cash proceeds from certain capital events				45.45%
Credit agreement, frequency of periodic payment				monthly
Principal amortization payments				$ 1,090,000.00
Credit Agreements | 2018 Term Loan Facility | Minimum
Debt Instrument [Line Items]
Net cash proceeds from capital events				150,000,000
Unrestricted cash				50,000,000.0
Credit Agreements | 2014 Seven Year Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 250,000,000.0
Credit Agreements | Bridge Facility
Debt Instrument [Line Items]
Maximum borrowing capacity						$ 30,000,000.0
Agreement suspension period extend date				Oct. 31, 2020
Debt instrument, maturity date				Oct. 31, 2020
Ability request additional commitment amount				$ 25,000,000.0
Outstanding line of credit				22,500,000
Credit Agreements | Bridge Facility | Subsequent Event
Debt Instrument [Line Items]
Increase in aggregate amount of commitments	$ 25,000,000.0
Credit Agreements | Term Loans
Debt Instrument [Line Items]
Outstanding borrowings				$ 560,500,000
Debt instrument, payment terms				7 years
Principal amortization payments				$ 909,000