Loans and Allowance for Loan Losses - Schedule of Composition of Loan (Detail) (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Commercial Loan [Member] \| Direct Finance Leases [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 50.0	$ 60.0

Amount, before allowance for credit loss, of financing receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919230-210447

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