The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Amount of income (loss) for proportionate share of equity method investee's income (loss).

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Amount of consolidated retained earnings that represent undistributed (not yet received) earnings from 50% or less owned persons accounted for by the equity method (equity method investees).

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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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Percentage of voting equity interests acquired in a business combination achieved in stages, excluding equity interests in the acquiree held by the acquirer immediately before the acquisition date.

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The maximum useful life of the basis difference assigned to finite-lived intangible assets in 'PnYnMdDTnHnMnS' format (the basis difference defined as the difference between the amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee).

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The weighted average amortization period of the basis difference assigned to finite-lived intangible assets, in 'PnYnMdDTnHnMnS' format (the basis difference defined as the difference between the amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee).

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The net of transaction cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

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The maximum useful life of the portion of the basis difference assigned to tangible assets, in 'PnYnMdDTnHnMnS' format (the basis difference defined as the difference between the amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee).

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The weighted average amortization period of the basis difference assigned to tangible assets, in 'PnYnMdDTnHnMnS' format (the basis difference defined as the difference between the amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee).

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Equity Method Investments and Related-Party Transactions - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2017	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Mar. 31, 2021	Apr. 30, 2021
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments			$ (317,000)	$ (256,000)	$ 14,000
Euro Infrastructure Co Step Acquisition [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of additional interest in subsidiary acquired							51.00%
Euro Infrastructure Co [Member]
Schedule of Equity Method Investments [Line Items]
Payments, net of transaction costs, to acquire the issued shares in investment	$ 139,500,000
Equity method investment ownership percentage	49.00%
Maximum useful life of intangible assets basis difference, years						11 years
Weighted average useful life of intangible assets basis difference, years						10 years
Maximum useful life of tangible assets basis difference, years						11 years
Weighted average useful life of tangible assets basis difference, years						11 years
Earnings from equity method investments		$ 0
Retained earnings of undistributed cumulative earnings in equity interests, net of tax							$ 10,400,000