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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues:
Gross premiums written	$ 126,054	$ 133,569	$ 393,699	$ 429,254
Net premiums written	109,045	115,051	344,348	357,233
Net premiums earned	108,619	119,553	328,818	358,993
Net investment income	10,134	8,795	27,618	25,103
Net realized investment gains (losses)	(963)	1,928	(850)	(9,057)
Other income (loss)	2,294	7,852	5,444	9,603
Total revenues	120,084	138,128	361,030	384,642
Losses and Expenses:
Net losses and loss adjustment expenses	82,395	72,162	202,656	215,057
Acquisition costs and other underwriting expenses	45,002	48,129	135,010	148,761
Corporate and other operating expenses	4,630	5,006	11,045	13,064
Interest expense	4,836	2,233	12,065	6,677
Income (loss) before income taxes	(16,779)	10,598	254	1,083
Non-U.S. Subsidiaries
Revenues:
Gross premiums written	50,812	51,900	164,975	141,297
Net premiums written	50,800	51,900	164,947	141,283
Net premiums earned	50,392	54,155	150,384	162,594
Net investment income	14,631	11,556	41,519	36,791
Net realized investment gains (losses)	(150)	58	87	128
Other income (loss)	40	(10)	213	17
Total revenues	64,913	65,759	192,203	199,530
Losses and Expenses:
Net losses and loss adjustment expenses	31,044	27,932	74,780	84,154
Acquisition costs and other underwriting expenses	21,922	24,651	65,544	71,758
Corporate and other operating expenses	1,807	2,906	4,137	7,181
Interest expense	4,679	2,081	11,653	6,233
Income (loss) before income taxes	5,461	8,189	36,089	30,204
U.S. Subsidiaries
Revenues:
Gross premiums written	114,076	123,770	348,331	394,312
Net premiums written	58,245	63,151	179,401	215,950
Net premiums earned	58,227	65,398	178,434	196,399
Net investment income	6,584	5,828	16,786	13,888
Net realized investment gains (losses)	(813)	1,870	(937)	(9,185)
Other income (loss)	2,254	7,862	5,231	9,586
Total revenues	66,252	80,958	199,514	210,688
Losses and Expenses:
Net losses and loss adjustment expenses	51,351	44,230	127,876	130,903
Acquisition costs and other underwriting expenses	23,080	23,478	69,466	77,003
Corporate and other operating expenses	2,823	2,100	6,908	5,883
Interest expense	11,238	8,741	31,099	26,020
Income (loss) before income taxes	(22,240)	2,409	(35,835)	(29,121)
Eliminations
Revenues:
Gross premiums written	(38,834)	(42,101)	(119,607)	(106,355)
Net investment income	(11,081)	(8,589)	(30,687)	(25,576)
Total revenues	(11,081)	(8,589)	(30,687)	(25,576)
Losses and Expenses:
Interest expense	$ (11,081)	$ (8,589)	$ (30,687)	$ (25,576)