Goodwill, Intangible Assets and Deferred Charge - Summary of Gross Carrying Value, Accumulated Amortization and Net Carrying Value of Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Intangible Assets [Line Items]
Intangible assets with an indefinite life, Carrying Value	$ 87,031	$ 87,031	$ 63,000
Deferred charge on retroactive reinsurance, Gross Carrying Value	271,176
Deferred charge on retroactive reinsurance, Accumulated Amortization	(15,265)
Deferred charge on retroactive reinsurance, Net Carrying Value	255,911
Fair Value Adjustments
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	366,668	342,701
Accumulated Amortization	(185,938)	(183,606)
Intangible assets with a definite life, Net Carrying Value	180,730	159,095	223,947
Losses and LAE liabilities
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	456,110	449,986
Accumulated Amortization	(307,785)	(299,413)
Intangible assets with a definite life, Net Carrying Value	148,325	150,573
Reinsurance balances recoverable
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	(175,774)	(193,617)
Accumulated Amortization	154,619	140,667
Intangible assets with a definite life, Net Carrying Value	(21,155)	(52,950)
Policy benefits for life and annuity contracts
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	86,332	86,332
Accumulated Amortization	(32,772)	(24,860)
Intangible assets with a definite life, Net Carrying Value	53,560	61,472
Other
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	47,000	47,000
Accumulated Amortization	(15,798)	(5,952)
Intangible assets with a definite life, Net Carrying Value	31,202	41,048	$ 27,000
Distribution channel
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	20,000	20,000
Accumulated Amortization	(2,777)	(1,444)
Intangible assets with a definite life, Net Carrying Value	17,223	18,556
Technology
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	15,000	15,000
Accumulated Amortization	(6,561)	(3,125)
Intangible assets with a definite life, Net Carrying Value	8,439	11,875
Brand
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	12,000	12,000
Accumulated Amortization	(6,460)	(1,383)
Intangible assets with a definite life, Net Carrying Value	5,540	10,617
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