Summary of Significant Accounting Policies - Narrative (Details)	3 Months Ended						12 Months Ended
	Dec. 31, 2021 USD ($) $ / shares shares	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($) $ / shares	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2021 USD ($) segment $ / shares shares	Dec. 31, 2020 USD ($) $ / shares	Dec. 31, 2019 USD ($)	Jun. 30, 2021 shares	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Property, Plant and Equipment [Line Items]
Interest expense							$ 19,090,000	$ 19,140,000	$ 17,157,000
Bad debt expense							0		0
Termination fees							$ 1,400,000
Weighted average remaining lease term							6 years 10 months 24 days
Tenant reimbursements		$ 300,000
Contingent revenue recognized during the period							$ 500,000	100,000	100,000
Intangible assets									0
Gain on dispositions of real estate investments							0	0	0
Impairment charges							$ 1,500,000	0	0
Number of reportable segments | segment							1
Accumulated Amortization	$ 9,051,000		$ 11,935,000				$ 9,051,000	11,935,000
Cash and cash equivalents and restricted cash	28,428,000		39,994,000				28,428,000	39,994,000	58,297,000			$ 54,801,000
Cash in excess of FDIC limit	26,300,000		38,200,000				26,300,000	38,200,000
Revenue from tenants	$ 1,500,000						70,219,000	62,895,000	70,530,000
Income tax expense							37,000	0	0
Revenues		$ 300,000
REIT taxable income							$ 0	$ 0	0
Dividends declared per common share (in dollars per share) | $ / shares	$ 0.10			$ 0.04889			$ 0.40	$ 0.04889
Uncertain tax positions	$ 0						$ 0
Operating lease right-of-use asset	55,167,000		55,375,000				55,167,000	$ 55,375,000			$ 54,900,000
Operating lease liability	54,770,000		54,820,000				54,770,000	54,820,000			54,900,000
Below market ground lease intangible asset reclassified as a result of adoption of new accounting guidance	$ 42,239,000		50,923,000				$ 42,239,000	50,923,000
Tenant Receivable
Property, Plant and Equipment [Line Items]
Bad debt expense								8,500,000
Error correction
Property, Plant and Equipment [Line Items]
Interest expense			600,000	$ 300,000	$ 200,000	$ 100,000
Depreciation expense			300,000
Class A Units
Property, Plant and Equipment [Line Items]
Investment owned, balance (in shares) | shares	37						37
Class B Units
Property, Plant and Equipment [Line Items]
Investment owned, balance (in shares) | shares										13,100
Below-market ground lease
Property, Plant and Equipment [Line Items]
Accumulated Amortization	$ 7,900,000		$ 1,800,000				$ 7,900,000	$ 1,800,000
Accounting Standards Update 2016-02
Property, Plant and Equipment [Line Items]
Straight-line rent liability reclassified as a result of adoption of new accounting guidance											2,700,000
Prepaid rent reclassified as a result of adoption of new accounting guidance											1,200,000
Accounting Standards Update 2016-02 | Below-market ground lease
Property, Plant and Equipment [Line Items]
Below market ground lease intangible asset reclassified as a result of adoption of new accounting guidance											$ 2,400,000
Return of Capital
Property, Plant and Equipment [Line Items]
Dividends, percent							100.00%	100.00%
Dividends declared per common share (in dollars per share) | $ / shares							$ 0.40
Tenant Reimbursement and Other Revenue
Property, Plant and Equipment [Line Items]
Tenant reimbursements									100,000
Revenues									$ 100,000
Building
Property, Plant and Equipment [Line Items]
Useful life							40 years
Land Improvements
Property, Plant and Equipment [Line Items]
Useful life							15 years
Furniture and Fixtures | Minimum
Property, Plant and Equipment [Line Items]
Useful life							5 years
Furniture and Fixtures | Maximum
Property, Plant and Equipment [Line Items]
Useful life							7 years