Fair Value Measurements - Summarizes Carrying Value and Estimated Fair Values of Financial Instruments not Carried at Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Surplus note	$ 8,088	$ 8,456
Surplus Note \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Estimated fair value	$ 7,876	$ 8,291

Financial instruments issued by insurance entities (surplus notes) that are includable in surplus for statutory accounting purposes as prescribed or permitted by state laws and regulations that are liabilities of the issuer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 470
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6486086&loc=d3e24387-158525

Name:	us-gaap_SurplusNotes
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant