Goodwill, Intangible Assets and Deferred Charge - Summary of Gross Carrying Value, Accumulated Amortization and Net Carrying Value of Intangible Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule Of Intangible Assets [Line Items]
Intangible assets with an indefinite life, Carrying Value	$ 87,031	$ 87,031
Deferred charge on retroactive reinsurance, Gross Carrying Value	271,176	271,176
Deferred charge on retroactive reinsurance, Accumulated Amortization	(16,876)	(15,265)
Deferred charge on retroactive reinsurance, Net Carrying Value	254,300	255,911
Fair Value Adjustments
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	368,610	366,668
Accumulated Amortization	(184,603)	(185,938)
Intangible assets with a definite life, Net Carrying Value	184,007	180,730
Losses and LAE liabilities
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	458,202	456,110
Accumulated Amortization	(306,417)	(307,785)
Intangible assets with a definite life, Net Carrying Value	151,785	148,325
Reinsurance balances recoverable
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	(175,924)	(175,774)
Accumulated Amortization	156,317	154,619
Intangible assets with a definite life, Net Carrying Value	(19,607)	(21,155)
Policy benefits for life and annuity contracts
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	86,332	86,332
Accumulated Amortization	(34,503)	(32,772)
Intangible assets with a definite life, Net Carrying Value	51,829	53,560
Other
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	42,000	42,000
Accumulated Amortization	(14,214)	(10,798)
Intangible assets with a definite life, Net Carrying Value	27,786	31,202
Distribution channel
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	20,000	20,000
Accumulated Amortization	(3,111)	(2,777)
Intangible assets with a definite life, Net Carrying Value	16,889	17,223
Technology
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	15,000	15,000
Accumulated Amortization	(9,470)	(6,561)
Intangible assets with a definite life, Net Carrying Value	5,530	8,439
Brand
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	7,000	7,000
Accumulated Amortization	(1,633)	(1,460)
Intangible assets with a definite life, Net Carrying Value	5,367	5,540
Syndicate capacity
Schedule Of Intangible Assets [Line Items]
Intangible assets with an indefinite life, Carrying Value	37,031	37,031
Licenses
Schedule Of Intangible Assets [Line Items]
Intangible assets with an indefinite life, Carrying Value	19,900	19,900
Management contract
Schedule Of Intangible Assets [Line Items]
Intangible assets with an indefinite life, Carrying Value	$ 30,100	$ 30,100