Losses and Loss Adjustment Expenses - Net (Reduction) Increase in Ultimate Losses and Loss Adjustment Expense Liabilities (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Prior Period
Net losses paid, Prior Period	$ 203,010	$ 194,485	$ 389,413	$ 312,641
Net incurred losses and LAE, prior periods	(30,172)	(55,435)	(62,256)	(98,313)
Current Period
Net losses paid, Current Period	17,022	21,490	22,356	32,654
Net incurred losses and LAE, current period	126,634	121,335	241,936	234,349
Total
Net losses paid	220,032	215,975	411,769	345,295
Net change in case and LAE reserves	(50,789)	(57,465)	(148,691)	(67,270)
Net change in IBNR reserves	(82,013)	(76,461)	(82,098)	(91,810)
Increase (reduction) in estimates of net ultimate losses	87,230	82,049	180,980	186,215
Increase (reduction) in provisions for bad debt	(5,184)	(625)	(6,630)	(20,439)
Increase (reduction) in provisions for unallocated LAE	(5,763)	(6,664)	(12,459)	(20,045)
Amortization of fair value adjustments	20,179	(8,860)	17,789	(9,695)
Total net incurred losses and LAE	96,462	65,900	179,680	136,036
Non-Life Run-Off
Prior Period
Net losses paid, Prior Period	140,998	155,006	271,321	215,695
Net change in case and LAE reserves, Prior Period	(74,832)	(108,819)	(183,801)	(118,813)
Net change in IBNR reserves, Prior Period	(101,240)	(84,581)	(141,753)	(135,020)
Increase (reduction) in estimates of net ultimate losses, Prior Period	(35,074)	(38,394)	(54,233)	(38,138)
Increase (reduction) in provisions for bad debt, Prior Period	(5,184)	(625)	(6,630)	(20,439)
Increase (reduction) in provisions for unallocated loss adjustment expense liabilities, Prior Period	(6,355)	(7,711)	(14,590)	(21,686)
Amortization of fair value adjustments, Prior Period	21,405	(4,687)	20,622	(4,980)
Net incurred losses and LAE, prior periods	(25,208)	(51,417)	(54,831)	(85,243)
Current Period
Net losses paid, Current Period	2,058	9,434	4,048	14,005
Net change in case and LAE reserves, Current Period	272	4,489	456	7,483
Net change in IBNR reserves, Current Period	(1,596)	8,624	1,854	21,785
Increase (reduction) in estimates of net ultimate losses, Current Period	734	22,547	6,358	43,273
Increase (reduction) in provisions for bad debt, Current Period	0	0	0	0
Increase (reduction) in provisions for unallocated loss adjustment expense liabilities, Current Period	(216)	0	229	0
Amortization of fair value adjustments, Current Period	0	0	0	0
Net incurred losses and LAE, current period	518	22,547	6,587	43,273
Total
Net losses paid	143,056	164,440	275,369	229,700
Net change in case and LAE reserves	(74,560)	(104,330)	(183,345)	(111,330)
Net change in IBNR reserves	(102,836)	(75,957)	(139,899)	(113,235)
Increase (reduction) in estimates of net ultimate losses	(34,340)	(15,847)	(47,875)	5,135
Increase (reduction) in provisions for bad debt	(5,184)	(625)	(6,630)	(20,439)
Increase (reduction) in provisions for unallocated LAE	(6,571)	(7,711)	(14,361)	(21,686)
Amortization of fair value adjustments	21,405	(4,687)	20,622	(4,980)
Total net incurred losses and LAE	(24,690)	(28,870)	(48,244)	(41,970)
Atrium
Prior Period
Net losses paid, Prior Period	7,268	7,583	12,778	16,624
Net change in case and LAE reserves, Prior Period	(3,391)	(3,946)	(7,351)	(7,657)
Net change in IBNR reserves, Prior Period	(6,181)	(3,560)	(7,772)	(16,553)
Increase (reduction) in estimates of net ultimate losses, Prior Period	(2,304)	77	(2,345)	(7,586)
Increase (reduction) in provisions for unallocated loss adjustment expense liabilities, Prior Period	(118)	(137)	(189)	(332)
Amortization of fair value adjustments, Prior Period	(1,013)	(3,678)	(1,375)	(3,678)
Net incurred losses and LAE, prior periods	(3,435)	(3,738)	(3,909)	(11,596)
Current Period
Net losses paid, Current Period	5,255	4,538	7,493	7,408
Net change in case and LAE reserves, Current Period	5,426	4,082	7,614	6,774
Net change in IBNR reserves, Current Period	9,719	8,746	21,201	17,929
Increase (reduction) in estimates of net ultimate losses, Current Period	20,400	17,366	36,308	32,111
Increase (reduction) in provisions for unallocated loss adjustment expense liabilities, Current Period	168	129	323	262
Amortization of fair value adjustments, Current Period	0	0	0	0
Net incurred losses and LAE, current period	20,568	17,495	36,631	32,373
Total
Net losses paid	12,523	12,121	20,271	24,032
Net change in case and LAE reserves	2,035	136	263	(883)
Net change in IBNR reserves	3,538	5,186	13,429	1,376
Increase (reduction) in estimates of net ultimate losses	18,096	17,443	33,963	24,525
Increase (reduction) in provisions for bad debt	0	0	0	0
Increase (reduction) in provisions for unallocated LAE	50	(8)	134	(70)
Amortization of fair value adjustments	(1,013)	(3,678)	(1,375)	(3,678)
Total net incurred losses and LAE	17,133	13,757	32,722	20,777
StarStone
Prior Period
Net losses paid, Prior Period	54,744	31,896	105,314	80,322
Net change in case and LAE reserves, Prior Period	(26,737)	6,397	(22,102)	(3,934)
Net change in IBNR reserves, Prior Period	(28,321)	(38,584)	(83,234)	(76,262)
Increase (reduction) in estimates of net ultimate losses, Prior Period	(314)	(291)	(22)	126
Increase (reduction) in provisions for unallocated loss adjustment expense liabilities, Prior Period	(1,002)	506	(2,036)	(563)
Amortization of fair value adjustments, Prior Period	(213)	(495)	(1,458)	(1,037)
Net incurred losses and LAE, prior periods	(1,529)	(280)	(3,516)	(1,474)
Current Period
Net losses paid, Current Period	9,709	7,518	10,815	11,241
Net change in case and LAE reserves, Current Period	48,473	40,332	56,493	48,877
Net change in IBNR reserves, Current Period	45,606	32,894	127,606	96,311
Increase (reduction) in estimates of net ultimate losses, Current Period	103,788	80,744	194,914	156,429
Increase (reduction) in provisions for unallocated loss adjustment expense liabilities, Current Period	1,760	549	3,804	2,274
Amortization of fair value adjustments, Current Period	0	0	0	0
Net incurred losses and LAE, current period	105,548	81,293	198,718	158,703
Total
Net losses paid	64,453	39,414	116,129	91,563
Net change in case and LAE reserves	21,736	46,729	34,391	44,943
Net change in IBNR reserves	17,285	(5,690)	44,372	20,049
Increase (reduction) in estimates of net ultimate losses	103,474	80,453	194,892	156,555
Increase (reduction) in provisions for bad debt	0	0	0	0
Increase (reduction) in provisions for unallocated LAE	758	1,055	1,768	1,711
Amortization of fair value adjustments	(213)	(495)	(1,458)	(1,037)
Total net incurred losses and LAE	$ 104,019	$ 81,013	$ 195,202	$ 157,229