Note Guarantees (Indemnification, Representations and Warranties related to loans sold) - Additional Information (Detail) - USD ($)	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Securitization \| Guarantee on loans sold or serviced with representation and warranties
Guarantor Obligations
Repurchased Loans	$ 0	$ 9,000,000

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