Summary of Significant Accounting Policies - Narrative (Details)	1 Months Ended				3 Months Ended		9 Months Ended
	May 31, 2019 USD ($)	Apr. 30, 2019 $ / shares shares	Sep. 30, 2018 USD ($) $ / shares shares	Mar. 31, 2018 $ / shares shares	Sep. 30, 2019 USD ($) shares	Sep. 30, 2018 USD ($) shares	Sep. 30, 2019 USD ($) shares	Sep. 30, 2018 USD ($) shares	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Accounting Policies [Line Items]
Amortization of above and below Market Leases					$ 3,400,000	$ 3,000,000.0	$ 9,882,000	$ 7,794,000
Number of Reportable Segments							1
Number Of Real Estate Properties Held-For-Sale					2		2
Cash in Excess of FDIC Insured Amounts					$ 9,700,000		$ 9,700,000			$ 52,700,000
Deferred Rent Receivables, Net					$ 21,300,000		$ 21,300,000			16,700,000
Incremental Common Shares Attributable to Dilutive Effect of Equity Forward Agreements | shares					376,558		529,893
Deferred income tax liability										475,000
Income tax expense					$ (184,000)	$ (125,000)	$ (210,000)	(391,000)
Proceeds From Issuance Of Common Stock							276,960,000	$ 159,604,000
Right of use assets					16,200,000		16,200,000
Lease liabilities					$ 16,310,000		$ 16,310,000
ASU 2016-02 | Restatement
Accounting Policies [Line Items]
Right of use assets									$ 7,500,000
Lease liabilities									$ 7,500,000
March 2018 Forward Sale [Member]
Accounting Policies [Line Items]
Forward Contract Indexed to Issuer's Equity, Shares | shares				3,450,000
Forward Contract Indexed to Issuer's Equity, Additional Shares | shares				450,000
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares				$ 48.00
Incremental Common Shares Attributable to Dilutive Effect of Equity Forward Agreements | shares						439,761		265,048
Proceeds From Issuance Of Common Stock			$ 160,200,000
September 2018 Forward Sales
Accounting Policies [Line Items]
Forward Contract Indexed to Issuer's Equity, Shares | shares			3,500,000
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares			$ 55.20
Incremental Common Shares Attributable to Dilutive Effect of Equity Forward Agreements | shares						8,455	359,713	2,818
Proceeds From Issuance Of Common Stock	$ 186,000,000.0
April 2019 Forward Equity
Accounting Policies [Line Items]
Forward Contract Indexed to Issuer's Equity, Shares | shares		3,162,500
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares		$ 65.85
Incremental Common Shares Attributable to Dilutive Effect of Equity Forward Agreements | shares					376,558	0	170,180	0
Unbilled Revenues
Accounting Policies [Line Items]
Accounts Receivable, Gross					$ 2,800,000		$ 2,800,000			$ 3,300,000