Income (Loss) Before Income Taxes from its Non-U.S. Subsidiaries and U.S. Subsidiaries (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues:
Gross written premiums	$ 143,749	$ 157,177	$ 464,022	$ 478,699
Net written premiums	130,611	138,836	416,987	421,321
Net earned premiums	140,302	133,312	426,617	383,602
Net investment income	11,746	11,348	19,516	32,393
Net realized investment gains (losses)	7,323	(2,690)	(22,332)	11,290
Other income (loss)	542	264	1,473	1,274
Total revenues	159,913	142,234	425,274	428,559
Losses and Expenses:
Net losses and loss adjustment expenses	97,148	73,583	242,092	201,979
Acquisition costs and other underwriting expenses	53,268	53,366	163,258	153,643
Corporate and other operating expenses	21,196	3,858	34,037	11,702
Interest expense	3,620	5,023	13,197	15,088
Loss on extinguishment of debt	3,060	0	3,060	0
Income (loss) before income taxes	(18,379)	6,404	(30,370)	46,147
Non-U.S. Subsidiaries
Revenues:
Gross written premiums	13,085	19,980	46,654	69,588
Net written premiums	13,085	19,990	46,654	69,591
Net earned premiums	9,983	19,512	53,384	52,798
Net investment income	4,054	7,212	17,336	22,254
Net realized investment gains (losses)	1,511	375	(3,867)	1,768
Other income (loss)	164	(234)	148	(256)
Total revenues	15,712	26,865	67,001	76,564
Losses and Expenses:
Net losses and loss adjustment expenses	519	7,628	12,874	24,076
Acquisition costs and other underwriting expenses	3,584	6,201	17,828	16,556
Corporate and other operating expenses	17,283	1,514	23,357	4,822
Interest expense	193	351	869	1,059
Loss on extinguishment of debt	3,060		3,060
Income (loss) before income taxes	(8,927)	11,171	9,013	30,051
U.S. Subsidiaries
Revenues:
Gross written premiums	130,664	137,197	417,368	409,111
Net written premiums	117,526	118,846	370,333	351,730
Net earned premiums	130,319	113,800	373,233	330,804
Net investment income	9,851	7,732	11,324	20,824
Net realized investment gains (losses)	5,812	(3,065)	(18,465)	9,522
Other income (loss)	378	498	1,325	1,530
Total revenues	146,360	118,965	367,417	362,680
Losses and Expenses:
Net losses and loss adjustment expenses	96,629	65,955	229,218	177,903
Acquisition costs and other underwriting expenses	49,684	47,165	145,430	137,087
Corporate and other operating expenses	3,913	2,344	10,680	6,880
Interest expense	5,586	8,268	21,472	24,714
Loss on extinguishment of debt	0		0
Income (loss) before income taxes	(9,452)	(4,767)	(39,383)	16,096
Eliminations
Revenues:
Gross written premiums	0	0	0	0
Net written premiums	0	0	0	0
Net earned premiums	0	0	0	0
Net investment income	(2,159)	(3,596)	(9,144)	(10,685)
Net realized investment gains (losses)	0	0	0	0
Other income (loss)	0	0	0	0
Total revenues	(2,159)	(3,596)	(9,144)	(10,685)
Losses and Expenses:
Net losses and loss adjustment expenses	0	0	0	0
Acquisition costs and other underwriting expenses	0	0	0	0
Corporate and other operating expenses	0	0	0	0
Interest expense	(2,159)	(3,596)	(9,144)	(10,685)
Loss on extinguishment of debt	0		0
Income (loss) before income taxes	$ 0	$ 0	$ 0	$ 0