Losses and Loss Adjustment Expenses - Net (Reduction) Increase in Ultimate Losses and Loss Adjustment Expense Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Effects of Reinsurance [Line Items]
Net losses paid	$ 781,889	$ 587,511	$ 401,496
Net change in case and LAE reserves	(278,825)	(275,494)	(290,554)
Net change in IBNR reserves	(324,026)	(231,357)	(232,931)
Increase (reduction) in estimates of net ultimate losses	179,038	80,660	(121,989)
(Reduction) Increase in provisions for bad debt	(25,271)	(7,700)	1,999
Increase (reduction) in provisions for unallocated LAE	(59,199)	(53,970)	(49,629)
Amortization of fair value adjustments	9,765	(9,844)	5,947
Net incurred losses and LAE	104,333	9,146	(163,672)
Prior periods	(372,031)	(318,671)	(257,114)
Current period	476,364	327,817	93,442
Non-Life Run-Off Segment
Effects of Reinsurance [Line Items]
Net losses paid	517,295	400,096	370,870
Net change in case and LAE reserves	(355,335)	(310,414)	(280,933)
Net change in IBNR reserves	(364,774)	(301,784)	(231,278)
Increase (reduction) in estimates of net ultimate losses	(202,814)	(212,102)	(141,341)
(Reduction) Increase in provisions for bad debt	(25,271)	(7,700)	1,999
Increase (reduction) in provisions for unallocated LAE	(62,653)	(48,891)	(49,580)
Amortization of fair value adjustments	19,908	3,982	5,947
Net incurred losses and LAE	(270,830)	(264,711)	(182,975)
Net losses paid, Prior Period	501,246	312,415	360,214
Net change in case and LAE reserves, Prior Period	(366,262)	(285,814)	(310,488)
Net change in IBNR reserves, Prior Period	(377,722)	(262,384)	(265,206)
(Reduction) increase in estimates of net ultimate losses, Prior Period	(242,738)	(235,783)	(215,480)
(Reduction) increase in provisions for bad debt, Prior Period	(25,271)	(7,700)	1,999
(Reduction) increase in provisions for unallocated loss adjustment expense liabilities, Prior Period	(62,653)	(49,445)	(49,580)
Amortization of fair value adjustments, Prior Period	19,908	3,982	5,947
Prior periods	(310,754)	(288,946)	(257,114)
Net losses paid, Current Period	16,049	87,681	10,656
Net change in case and LAE reserves, Current Period	10,927	(24,600)	29,555
Net change in IBNR reserves, Current Period	12,948	(39,400)	33,928
(Reduction) increase in estimates of net ultimate losses, Current Period	39,924	23,681	74,139
(Reduction) increase in provisions for bad debt, Current Period	0	0	0
(Reduction) increase in provisions for unallocated loss adjustment expense liabilities, Current Period	0	554	0
Amortization of fair value adjustments, Current Period	0	0	0
Current period	39,924	24,235	74,139
Atrium
Effects of Reinsurance [Line Items]
Net losses paid	52,035	57,611	30,626
Net change in case and LAE reserves	(709)	(2,684)	(9,621)
Net change in IBNR reserves	2,844	11,557	(1,653)
Increase (reduction) in estimates of net ultimate losses	54,170	66,484	19,352
(Reduction) Increase in provisions for bad debt	0	0	0
Increase (reduction) in provisions for unallocated LAE	(83)	9	(49)
Amortization of fair value adjustments	(6,608)	(11,065)	0
Net incurred losses and LAE	47,479	55,428	19,303
Net losses paid, Prior Period	30,890	27,985	0
Net change in case and LAE reserves, Prior Period	(18,213)	(16,986)	0
Net change in IBNR reserves, Prior Period	(27,382)	(18,114)	0
(Reduction) increase in estimates of net ultimate losses, Prior Period	(14,705)	(7,115)	0
(Reduction) increase in provisions for unallocated loss adjustment expense liabilities, Prior Period	(608)	(486)	0
Amortization of fair value adjustments, Prior Period	(6,608)	(11,065)	0
Prior periods	(21,921)	(18,666)	0
Net losses paid, Current Period	21,145	29,626	30,626
Net change in case and LAE reserves, Current Period	17,504	14,302	(9,621)
Net change in IBNR reserves, Current Period	30,226	29,671	(1,653)
(Reduction) increase in estimates of net ultimate losses, Current Period	68,875	73,599	19,352
(Reduction) increase in provisions for unallocated loss adjustment expense liabilities, Current Period	525	495	(49)
Amortization of fair value adjustments, Current Period	0	0	0
Current period	69,400	74,094	19,303
StarStone Segment
Effects of Reinsurance [Line Items]
Net losses paid	212,559	129,804	0
Net change in case and LAE reserves	77,219	37,604	0
Net change in IBNR reserves	37,904	58,870	0
Increase (reduction) in estimates of net ultimate losses	327,682	226,278	0
(Reduction) Increase in provisions for bad debt	0	0	0
Increase (reduction) in provisions for unallocated LAE	3,537	(5,088)	0
Amortization of fair value adjustments	(3,535)	(2,761)	0
Net incurred losses and LAE	327,684	218,429	$ 0
Net losses paid, Prior Period	149,820	80,315
Net change in case and LAE reserves, Prior Period	15,772	24,208
Net change in IBNR reserves, Prior Period	(200,730)	(105,177)
(Reduction) increase in estimates of net ultimate losses, Prior Period	(35,138)	(654)
(Reduction) increase in provisions for unallocated loss adjustment expense liabilities, Prior Period	(683)	(7,644)
Amortization of fair value adjustments, Prior Period	(3,535)	(2,761)
Prior periods	(39,356)	(11,059)
Net losses paid, Current Period	62,739	49,489
Net change in case and LAE reserves, Current Period	61,447	13,396
Net change in IBNR reserves, Current Period	238,634	164,047
(Reduction) increase in estimates of net ultimate losses, Current Period	362,820	226,932
(Reduction) increase in provisions for unallocated loss adjustment expense liabilities, Current Period	4,220	2,556
Amortization of fair value adjustments, Current Period	0	0
Current period	$ 367,040	$ 229,488