Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	9 Months Ended
Sep. 30, 2019 USD ($) Trust Office Segment counties
Significant Of Accounting Policies [Line Items]
Number of subsidiary business trusts (in trusts) \| Trust	5
Number of loan production offices (in offices) \| Office	2
Company's investments in the trusts \| $	$ 1,717
Number of business segment (in segments) \| Segment	1
Loans contractual past due	90 days
California
Significant Of Accounting Policies [Line Items]
Number of counties (in counties) \| counties	29

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

No definition available.

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration