Schedule II. Condensed Financial Information of Registrant - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating activities
Net cash provided by operating activities	$ 37,979	$ 63,398	$ 78,824
Investing activities
Purchases of property and equipment	(1,296)	(921)	(1,018)
Net cash provided by investing activities	70,959	43,371	11,688
Financing activities
Proceeds from stock option exercises			20
Finance lease purchases	(44)	(50)	(47)
Dividends to shareholders	(99,929)	(88,775)	(87,016)
Net cash used in financing activities	(99,973)	(88,825)	(87,043)
Change in cash and cash equivalents	8,965	17,944	3,469
Cash and cash equivalents at beginning of year	61,757	43,813	40,344
Cash and cash equivalents at end of year	70,722	61,757	43,813
Parent Company [Member]
Operating activities
Net cash provided by operating activities	6,622	6,012	2,333
Investing activities
Purchases of investments	(87,289)	(10,982)	(27,140)
Proceeds from sales of investments	28,780	18,970	1,987
Purchases of property and equipment	(1,277)	(764)	(995)
Dividends from subsidiary	148,400	88,600	115,900
Net cash provided by investing activities	88,614	95,824	89,752
Financing activities
Proceeds from stock option exercises			20
Finance lease purchases	(44)	(50)	(47)
Dividends to shareholders	(99,929)	(88,775)	(87,016)
Net cash used in financing activities	(99,973)	(88,825)	(87,043)
Change in cash and cash equivalents	(4,737)	13,011	5,042
Cash and cash equivalents at beginning of year	23,562	10,551	5,509
Cash and cash equivalents at end of year	$ 18,825	$ 23,562	$ 10,551