Acquisitions - Purchase Price and Fair Value of Assets Acquired (Detail) $ in Thousands, € in Millions	Nov. 13, 2015 USD ($)	Nov. 13, 2015 EUR (€)	May. 05, 2015 USD ($)	Jan. 27, 2015 USD ($)	Apr. 01, 2014 USD ($)	Nov. 25, 2013 USD ($)	Sep. 09, 2013 USD ($)	Jul. 08, 2013 USD ($)	Mar. 31, 2013 USD ($)	Feb. 07, 2013 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Business Acquisition [Line Items]
Excess of purchase price over fair value of net assets acquired											$ 73,071	$ 73,071	$ 60,071
Nationale Suisse Assurance S.A.
Business Acquisition [Line Items]
Purchase price	$ 35,225	€ 32.8
Net assets acquired at fair value	35,225
Excess of purchase price over fair value of net assets acquired	$ 0
Wilton Relife Settlements
Business Acquisition [Line Items]
Purchase price			$ 173,058
Net assets acquired at fair value			173,058
Excess of purchase price over fair value of net assets acquired			$ 0
Sussex Insurance Company
Business Acquisition [Line Items]
Purchase price				$ 218,000
Net assets acquired at fair value				218,000
Excess of purchase price over fair value of net assets acquired				$ 0
StarStone
Business Acquisition [Line Items]
Purchase price					$ 656,088			$ 646,000
Net assets acquired at fair value					643,088
Excess of purchase price over fair value of net assets acquired					$ 13,000
Atrium
Business Acquisition [Line Items]
Purchase price						$ 158,000
Net assets acquired at fair value						119,152
Excess of purchase price over fair value of net assets acquired						$ 38,848
Arden
Business Acquisition [Line Items]
Purchase price							$ 79,600
Net assets acquired at fair value							$ 79,600
Pavonia
Business Acquisition [Line Items]
Purchase price									$ 155,564
Net assets acquired at fair value									$ 155,564
SeaBright
Business Acquisition [Line Items]
Purchase price										$ 252,091
Net assets acquired at fair value										$ 252,091