Schedule II - Condensed Financial Information of Registrant - Condensed Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
PREMIUMS EARNED AND OTHER REVENUES
Net investment income	$ 2,823	$ 4,557	$ 6,179	$ 6,834	$ 7,578	$ 7,613	$ 7,410	$ 8,142	$ 20,393	$ 30,743	$ 24,816
Net realized gains (losses) on investments		53,800							63,352	(12,715)	(2,089)
Net change in unrealized gains (losses) of equity securities									25	23,188	(17,169)
Other revenue									8,501	7,972	7,163
Total premiums earned and other revenues	273,126	311,665	252,704	235,275	239,402	229,641	233,722	236,586	1,072,770	939,351	823,816
OPERATING COSTS AND EXPENSES
General and administrative expenses									289,729	272,428	256,488
Total operating costs and expenses	300,125	315,457	225,266	207,691	308,455	201,745	182,792	182,842	1,048,539	875,834	670,943
Benefit from income taxes									5,126	17,003	35,822
NET INCOME	$ (17,675)	$ (3,169)	$ 19,882	$ 20,067	$ (51,073)	$ 20,146	$ 37,293	$ 40,148	19,105	46,514	117,051
Parent Company [Member]
PREMIUMS EARNED AND OTHER REVENUES
Net investment income									273	2,249	1,635
Net realized gains (losses) on investments									38	(1,908)	0
Net change in unrealized gains (losses) of equity securities									0	3,186	(2,648)
Management fee									166	166	157
Other revenue									16	10	0
Total premiums earned and other revenues									493	3,703	(856)
OPERATING COSTS AND EXPENSES
General and administrative expenses									15,448	21,526	32,063
Total operating costs and expenses									15,448	21,526	32,063
LOSS BEFORE INCOME TAXES AND EQUITY IN NET    EARNINGS OF SUBSIDIARIES									(14,955)	(17,823)	(32,919)
Benefit from income taxes									(215)	(2,984)	(10,434)
LOSS BEFORE EQUITY IN NET EARNINGS OF SUBSIDIARIES									(14,740)	(14,839)	(22,485)
Equity in net income of subsidiaries									33,828	61,336	139,987
NET INCOME									$ 19,088	$ 46,497	$ 117,502