Schedule III - Supplementary Insurance Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	$ 89,123	$ 61,706	$ 16,744
Reserves for Losses and Loss Adjustment Expenses	5,720,149	4,509,421	4,219,905
Unearned Premiums	542,771	468,626	70,697
Policy Benefits for Life and Annuity Contracts	1,304,697	1,220,864	1,273,100
Net Premiums Earned	839,071	646,450	239,807
Net Investment Income	157,654	117,369	93,295
Losses and Loss Expenses and Policy Benefits	201,259	117,192	(85,318)
Amortization of Deferred Acquisition Costs	177,430	132,573	23,199
Other Operating Expenses	422,549	371,374	219,248
Net Premiums Written	871,996	649,954	103,193
Operating Segments | Non-life Run-off
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	1,788	0	0
Reserves for Losses and Loss Adjustment Expenses	4,585,454	3,435,010	4,004,513
Unearned Premiums	27,792	197	1,199
Policy Benefits for Life and Annuity Contracts	0	0	0
Net Premiums Earned	44,369	31,168	112,611
Net Investment Income	84,185	67,432	64,048
Losses and Loss Expenses and Policy Benefits	(270,830)	(264,711)	(182,975)
Amortization of Deferred Acquisition Costs	8,860	8,393	14,379
Other Operating Expenses	257,926	213,571	191,268
Net Premiums Written	22,594	10,272	9,233
Operating Segments | Atrium
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	16,326	16,520	16,744
Reserves for Losses and Loss Adjustment Expenses	201,017	212,611	215,392
Unearned Premiums	59,808	61,030	65,804
Policy Benefits for Life and Annuity Contracts	0	0	0
Net Premiums Earned	134,675	135,945	32,212
Net Investment Income	2,225	1,971	521
Losses and Loss Expenses and Policy Benefits	47,479	55,428	19,303
Amortization of Deferred Acquisition Costs	45,509	43,417	0
Other Operating Expenses	36,087	38,791	9,660
Net Premiums Written	134,580	136,275	30,104
Operating Segments | StarStone Segment
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	71,009	45,186
Reserves for Losses and Loss Adjustment Expenses	933,678	861,800
Unearned Premiums	455,171	406,706
Policy Benefits for Life and Annuity Contracts	0	0
Net Premiums Earned	573,146	373,633
Net Investment Income	15,937	9,714
Losses and Loss Expenses and Policy Benefits	327,684	218,429
Amortization of Deferred Acquisition Costs	109,347	65,734
Other Operating Expenses	125,658	114,289
Net Premiums Written	628,427	399,174
Operating Segments | Life and Annuities
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	0	0	0
Reserves for Losses and Loss Adjustment Expenses	0	0	0
Unearned Premiums	0	693	3,694
Policy Benefits for Life and Annuity Contracts	1,304,697	1,220,864	1,273,100
Net Premiums Earned	86,881	105,704	94,984
Net Investment Income	56,541	39,470	30,182
Losses and Loss Expenses and Policy Benefits	96,926	108,046	78,354
Amortization of Deferred Acquisition Costs	13,714	15,029	8,820
Other Operating Expenses	17,925	18,412	22,452
Net Premiums Written	86,395	104,233	63,856
Eliminations
Supplementary Insurance Information, by Segment [Line Items]
Net Investment Income	(1,234)	(1,218)	(1,456)
Other Operating Expenses	(15,047)	(13,689)	(4,132)
Net Premiums Written	$ 0	$ 0	$ 0