Schedule of Total Investment Return (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Net investment income	$ 27,627	$ 37,020	$ 28,392
Net realized investment gains (losses)	(32,929)	15,887	(14,662)
Change in unrealized holding gains (losses)	(61,627)	(34,363)	21,779
Net realized and unrealized investment returns	(94,556)	(18,476)	7,117
Total investment return	$ (66,929)	$ 18,544	$ 35,509
Total investment return %	(4.70%)	1.20%	2.30%
Average investment portfolio	$ 1,437,327	$ 1,490,933	$ 1,528,425

Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(2))
-URI https://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Name:	us-gaap_NetInvestmentIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration