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Accounting Policies - Additional Information (Detail) - USD ($) | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Dec. 31, 2020 | Jan. 01, 2020
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Investment in direct financing leases, net | $ 74,895,000 |  | $ 74,895,000 |  | $ 77,238,000 |
Impairments | 756,000 | $ 507,000 | 1,532,000 | $ 1,538,000 |  |
Notes and mortgages receivable | $ 21,452,000 |  | $ 21,452,000 |  | 11,280,000 |
Level 3 [Member] |  |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Assumed annual average rent increases for unobservable inputs |  |  | 2.00% |  |  |
Level 3 [Member] | Measurement Input Expected Term [Member] | Maximum [Member] |  |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Assumed holding periods for unobservable inputs |  |  | 15 years |  |  |
Level 3 [Member] | Measurement Input Cap Rate [Member] |  |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Real estate fair value, measurement input | 8.00% |  | 8.00% |  |  |
Level 3 [Member] | Measurement Input Discount Rate [Member] |  |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Real estate fair value, measurement input | 7.00% |  | 7.00% |  |  |
Properties [Member] |  |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Impairments |  |  | $ 614,000 | 306,000 |  |
Estimated Sale Price Method [Member] |  |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Impairments |  |  | 43,000 |  |  |
Discounted Cash Flow Method [Member] |  |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Impairments |  |  | 0 |  |  |
Accumulation of Asset Retirement Cost Method [Member] |  |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Impairments |  |  | 1,489,000 |  |  |
Construction Loans [Member] |  |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Notes and mortgages receivable | $ 11,083,000 |  | 11,083,000 |  |  |
Notes and Mortgages Receivable [Member] |  |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Impairments | 0 | 0 | 0 | 0 |  |
Direct Financing Leases Financing Receivable [Member] |  |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Impairments | 0 | $ 0 | 0 | $ 0 |  |
Accounting Standards Update 2016-13 [Member] |  |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Investment in direct financing leases, net |  |  |  |  |  | $ 82,366,000
Estimated credit loss reserve related to direct financing leases |  |  |  |  |  | 578,000
Additional allowance for credit losses |  |  |  |  | 340,000 |
Credit loss reserve |  |  |  |  |  | 309,000
Notes and mortgages receivable |  |  |  |  |  | $ 30,855,000
Proceeds from construction loans |  |  | 11,083,000 |  |  |
Accounting Standards Update 2016-13 [Member] | Notes and Mortgages Receivable [Member] |  |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Additional allowance for credit losses | 0 |  | 0 |  | $ 28,000 |
Accounting Standards Update 2016-13 [Member] | Direct Financing Leases Financing Receivable [Member] |  |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |  |
Additional allowance for credit losses | $ 0 |  | $ 0 |  |  |

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