Losses and Loss Adjustment Expenses - Net (Reduction) Increase in Ultimate Losses and Loss Adjustment Expense Liabilities (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Effects of Reinsurance [Line Items]
Net losses paid	$ 191,737	$ 129,319
Net change in case and LAE reserves	(97,902)	(9,805)
Net change in IBNR reserves	(86)	(15,349)
Increase (reduction) in estimates of net ultimate losses	93,749	104,165
(Reduction) Increase in provisions for bad debt	(1,448)	(19,814)
Increase (reduction) in provisions for unallocated LAE	(6,693)	(13,381)
Amortization of fair value adjustments	(2,390)	(834)
Net incurred losses and LAE	83,218	70,136
Non-Life Run-Off Segment
Effects of Reinsurance [Line Items]
Net losses paid	132,313	65,260
Net change in case and LAE reserves	(108,785)	(7,000)
Net change in IBNR reserves	(37,063)	(37,278)
Increase (reduction) in estimates of net ultimate losses	(13,535)	20,982
(Reduction) Increase in provisions for bad debt	(1,448)	(19,814)
Increase (reduction) in provisions for unallocated LAE	(7,788)	(13,975)
Amortization of fair value adjustments	(783)	(293)
Net incurred losses and LAE	(23,554)	(13,100)
Net losses paid, Prior Period	130,323	60,689
Net change in case and LAE reserves, Prior Period	(108,969)	(9,994)
Net change in IBNR reserves, Prior Period	(40,513)	(50,439)
(Reduction) increase in estimates of net ultimate losses, Prior Period	(19,159)	256
(Reduction) increase in provisions for bad debt, Prior Period	(1,448)	(19,814)
(Reduction) increase in provisions for unallocated loss adjustment expense liabilities, Prior Period	(8,233)	(13,975)
Amortization of fair value adjustments, Prior Period	(783)	(293)
Prior periods	(29,623)	(33,826)
Net losses paid, Current Period	1,990	4,571
Net change in case and LAE reserves, Current Period	184	2,994
Net change in IBNR reserves, Current Period	3,450	13,161
(Reduction) increase in estimates of net ultimate losses, Current Period	5,624	20,726
(Reduction) increase in provisions for bad debt, Current Period	0	0
(Reduction) increase in provisions for unallocated loss adjustment expense liabilities, Current Period	445	0
Amortization of fair value adjustments, Current Period	0	0
Current period	6,069	20,726
Atrium
Effects of Reinsurance [Line Items]
Net losses paid	7,748	11,911
Net change in case and LAE reserves	(1,772)	(1,019)
Net change in IBNR reserves	9,891	(3,810)
Increase (reduction) in estimates of net ultimate losses	15,867	7,082
(Reduction) Increase in provisions for bad debt	0	0
Increase (reduction) in provisions for unallocated LAE	84	(62)
Amortization of fair value adjustments	(362)	0
Net incurred losses and LAE	15,589	7,020
Net losses paid, Prior Period	5,510	9,041
Net change in case and LAE reserves, Prior Period	(3,960)	(3,711)
Net change in IBNR reserves, Prior Period	(1,591)	(12,993)
(Reduction) increase in estimates of net ultimate losses, Prior Period	(41)	(7,663)
(Reduction) increase in provisions for unallocated loss adjustment expense liabilities, Prior Period	(70)	(195)
Amortization of fair value adjustments, Prior Period	(362)	0
Prior periods	(473)	(7,858)
Net losses paid, Current Period	2,238	2,870
Net change in case and LAE reserves, Current Period	2,188	2,692
Net change in IBNR reserves, Current Period	11,482	9,183
(Reduction) increase in estimates of net ultimate losses, Current Period	15,908	14,745
(Reduction) increase in provisions for unallocated loss adjustment expense liabilities, Current Period	154	133
Amortization of fair value adjustments, Current Period	0	0
Current period	16,062	14,878
StarStone Segment
Effects of Reinsurance [Line Items]
Net losses paid	51,676	52,148
Net change in case and LAE reserves	12,655	(1,786)
Net change in IBNR reserves	27,086	25,739
Increase (reduction) in estimates of net ultimate losses	91,417	76,101
(Reduction) Increase in provisions for bad debt	0	0
Increase (reduction) in provisions for unallocated LAE	1,011	656
Amortization of fair value adjustments	(1,245)	(541)
Net incurred losses and LAE	91,183	76,216
Net losses paid, Prior Period	50,570	48,425
Net change in case and LAE reserves, Prior Period	4,636	(10,331)
Net change in IBNR reserves, Prior Period	(54,913)	(37,677)
(Reduction) increase in estimates of net ultimate losses, Prior Period	293	417
(Reduction) increase in provisions for unallocated loss adjustment expense liabilities, Prior Period	(1,035)	(1,070)
Amortization of fair value adjustments, Prior Period	(1,245)	(541)
Prior periods	(1,987)	(1,194)
Net losses paid, Current Period	1,106	3,723
Net change in case and LAE reserves, Current Period	8,019	8,545
Net change in IBNR reserves, Current Period	81,999	63,416
(Reduction) increase in estimates of net ultimate losses, Current Period	91,124	75,684
(Reduction) increase in provisions for unallocated loss adjustment expense liabilities, Current Period	2,046	1,726
Amortization of fair value adjustments, Current Period	0	0
Current period	$ 93,170	$ 77,410