Impact of Recently Issued Accounting Standards - Additional Information (Detail) - Accounting Standards Update 2016-02 $ in Millions	Sep. 30, 2018 USD ($)
Minimum
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Additional operating lease liabilities	$ 75
Right of use assets	75
Maximum
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Additional operating lease liabilities	85
Right of use assets	$ 85