Goodwill and Intangible Assets - Summary of Gross Carrying Value, Accumulated Amortization and Net Carrying Value of Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	$ 434,701		$ 434,701
Intangible assets, Gross Carrying Value	497,701		497,701
Intangible assets, Accumulated Amortization	(1,500)	(2,100)	(183,754)
Accumulated Amortization	(183,088)		(183,754)
Intangible assets with a definite life, Net Carrying Value	251,613		250,947
Intangible assets, Net Carrying Value	314,613		313,947
Intangible assets with an indefinite life, Carrying Value	63,000		63,000
Atrium [Member]
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	27,000		27,000
Accumulated Amortization	(677)
Intangible assets with a definite life, Net Carrying Value	26,323		27,000
Atrium [Member] | Distribution Channel [Member]
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	20,000		20,000
Accumulated Amortization	(444)
Intangible assets with a definite life, Net Carrying Value	19,556		20,000
Atrium [Member] | Brand [Member]
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	7,000		7,000
Accumulated Amortization	(233)
Intangible assets with a definite life, Net Carrying Value	6,767		7,000
Fair Value Adjustments [Member]
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	407,701		407,701
Intangible assets, Accumulated Amortization	1,343
Accumulated Amortization	(182,411)		(183,754)
Intangible assets with a definite life, Net Carrying Value	225,290		223,947
Fair Value Adjustments [Member] | Losses and Loss Adjustment Expense [Member]
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	500,485		500,485
Accumulated Amortization	(288,550)		(282,178)
Intangible assets with a definite life, Net Carrying Value	211,935		218,307
Fair Value Adjustments [Member] | Reinsurance Balances Recoverable [Member]
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	(179,116)		(179,116)
Accumulated Amortization	124,096		113,659
Intangible assets with a definite life, Net Carrying Value	(55,020)		(65,457)
Fair Value Adjustments [Member] | Policy Benefits for Life and Annuity Contracts [Member]
Schedule Of Intangible Assets [Line Items]
Gross Carrying Value	86,332		86,332
Accumulated Amortization	(17,957)		(15,235)
Intangible assets with a definite life, Net Carrying Value	68,375		71,097
Syndicate Capacity [Member]
Schedule Of Intangible Assets [Line Items]
Intangible assets with an indefinite life, Carrying Value	32,900		32,900
Management Contract [Member]
Schedule Of Intangible Assets [Line Items]
Intangible assets with an indefinite life, Carrying Value	$ 30,100		$ 30,100