Loans - Additional Information (Detail) - Minimum	9 Months Ended
Sep. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of days past due for a loan to remain on accrual status	90 days
Number of days loans past due still accruing include purchased credit-impaired loans	90 days

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.

No definition available.

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