Derivative Financial Instruments - Additional Information (Detail)	12 Months Ended
Dec. 31, 2017 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on sale of mortgage banking business	$ 0

Gain (loss) from sale or disposal of an organization or integrated set of activities (for example, but not limited to, a partnership or corporation) engaged in providing a product or service in a commercial, industrial, or professional environment.

No definition available.

Name:	us-gaap_GainLossOnSaleOfBusiness
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration