Income Taxes - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018 USD ($)
Income Tax Contingency [Line Items]
Adjustments to provisional amounts due to Tax Act	$ 0
Tax cuts and jobs act of 2017, accounting complete	false
Internal Revenue Service [Member] | Earliest Tax Year [Member]
Income Tax Contingency [Line Items]
Open tax year	2011
Internal Revenue Service [Member] | Latest Tax Year [Member]
Income Tax Contingency [Line Items]
Open tax year	2014