Income Taxes - Additional Information (Detail)	9 Months Ended
Sep. 30, 2018 USD ($)
Income Tax Contingency [Line Items]
Cumulative effect on retained deficit	$ 0
Unrecognized tax benefits	$ 0
Earliest Tax Year [Member]
Income Tax Contingency [Line Items]
Open tax year	2004
Latest Tax Year [Member]
Income Tax Contingency [Line Items]
Open tax year	2016

Amount of the related income tax effect of a cumulative effect on retained earnings.

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Tax year that remains open to examination under enacted tax laws, in CCYY format.

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Amount of unrecognized tax benefits.

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