Components of net Investment in Direct Financing and Sales-Type Leases (Parenthetical) (Detail) - Customer	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Capital Leased Assets [Line Items]
Number of customers represent direct financing and sales-type leases portfolio	1	1
Customer One
Capital Leased Assets [Line Items]
Percentage of direct financing and sales-type leases portfolio	84.90%	80.10%

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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