Loans and Allowance for Loan Losses - Summary of Aging of Loans (Parenthetical) (Detail) $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($)
Receivables [Abstract]
loan premiums	$ 10,606
capitalized loan origination costs	$ 14,596

Amount of unearned premiums on outstanding advances made and reported by Federal Home Loan Bank (FHLBank).

No definition available.

Name:	us-gaap_FederalHomeLoanBankAdvancesPremium
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant