Income 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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues:
Gross premiums written	$ 157,177	$ 135,606	$ 478,699	$ 418,670
Net premiums written	138,836	116,233	421,321	360,557
Net premiums earned	133,312	120,528	383,602	342,447
Net investment income	11,348	11,750	32,393	34,108
Net realized investment gains (losses)	(2,690)	5,319	11,290	7,833
Other income (loss)	264	411	1,274	1,289
Total revenues	142,234	138,008	428,559	385,677
Losses and Expenses:
Net losses and loss adjustment expenses	73,583	80,493	201,979	195,426
Acquisition costs and other underwriting expenses	53,366	48,680	153,643	141,196
Corporate and other operating expenses	3,858	3,475	11,702	23,653
Interest expense	5,023	4,924	15,088	14,725
Income (loss) before income taxes	6,404	436	46,147	10,677
Non-U.S. Subsidiaries
Revenues:
Gross premiums written	19,980	9,361	69,588	39,976
Net premiums written	19,990	9,356	69,591	39,970
Net premiums earned	19,512	30,220	52,798	115,353
Net investment income	7,212	12,013	22,254	39,527
Net realized investment gains (losses)	375	(273)	1,768	(437)
Other income (loss)	(234)	(82)	(256)	(179)
Total revenues	26,865	41,878	76,564	154,264
Losses and Expenses:
Net losses and loss adjustment expenses	7,628	14,877	24,076	48,210
Acquisition costs and other underwriting expenses	6,201	13,188	16,556	50,475
Corporate and other operating expenses	1,514	1,237	4,822	10,550
Interest expense	351	356	1,059	6,749
Income (loss) before income taxes	11,171	12,220	30,051	38,280
U.S. Subsidiaries
Revenues:
Gross premiums written	137,197	126,245	409,111	378,694
Net premiums written	118,846	106,877	351,730	320,587
Net premiums earned	113,800	90,308	330,804	227,094
Net investment income	7,732	7,204	20,824	21,428
Net realized investment gains (losses)	(3,065)	5,592	9,522	8,270
Other income (loss)	498	493	1,530	1,468
Total revenues	118,965	103,597	362,680	258,260
Losses and Expenses:
Net losses and loss adjustment expenses	65,955	65,616	177,903	147,216
Acquisition costs and other underwriting expenses	47,165	35,492	137,087	90,721
Corporate and other operating expenses	2,344	2,238	6,880	13,103
Interest expense	8,268	12,035	24,714	34,823
Income (loss) before income taxes	(4,767)	(11,784)	16,096	(27,603)
Eliminations
Revenues:
Gross premiums written	0	0	0	0
Net premiums written	0	0	0	0
Net premiums earned	0	0	0	0
Net investment income	(3,596)	(7,467)	(10,685)	(26,847)
Net realized investment gains (losses)	0	0	0	0
Other income (loss)	0	0	0	0
Total revenues	(3,596)	(7,467)	(10,685)	(26,847)
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	(3,596)	(7,467)	(10,685)	(26,847)
Income (loss) before income taxes	$ 0	$ 0	$ 0	$ 0