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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Name:	us-gaap_FinancialStatementLineItemsWithDifferencesInReportedAmountAndReportingCurrencyDenominatedAmountsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Currency Exchange Rates (Detail)	Sep. 30, 2018 $ / shares	Sep. 30, 2018 ¥ / shares	Dec. 31, 2017 $ / shares	Dec. 31, 2017 ¥ / shares	Sep. 30, 2017 $ / shares	Sep. 30, 2017 ¥ / shares
Balance Sheet
Financial Statement Line Items with Differences in Reported Amount and Reporting Currency Denominated Amounts [Line Items]
Currency exchange rate used in creating the amounts included in balance sheet, statements of operations and cash \| (per share)	$ 1	¥ 6.8683	$ 1	¥ 6.5064	$ 1	¥ 6.6549
Statements of Operations and Cash Flows
Financial Statement Line Items with Differences in Reported Amount and Reporting Currency Denominated Amounts [Line Items]
Currency exchange rate used in creating the amounts included in balance sheet, statements of operations and cash \| (per share)	$ 1	¥ 6.5153	$ 1	¥ 6.7570	$ 1	¥ 6.8065