Acquisitions - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended		3 Months Ended													3 Months Ended						3 Months Ended
	Jul. 08, 2013	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Trident [Member]	Mar. 31, 2014 Atrium [Member] Minimum [Member]	Mar. 31, 2014 Atrium [Member] Maximum [Member]	Mar. 31, 2014 Torus Insurance Holdings Limited [Member]	Mar. 31, 2014 Corsair [Member]	Apr. 17, 2014 Subsequent Event [Member] Trident [Member]	Mar. 31, 2014 Share Capital - Ordinary Shares [Member]	Dec. 31, 2013 Share Capital - Ordinary Shares [Member]	Mar. 31, 2014 Share Capital - Ordinary Shares [Member] Torus Insurance Holdings Limited [Member]	Mar. 31, 2014 Series B Preferred Stock [Member]	Mar. 31, 2014 Kenmare [Member]	Mar. 31, 2014 Kenmare [Member] Torus Insurance Holdings Limited [Member]	Apr. 17, 2014 Kenmare [Member] Subsequent Event [Member]	Mar. 31, 2014 Bayshore [Member]	Mar. 31, 2014 Bayshore [Member] Trident [Member]	Mar. 31, 2014 Bayshore [Member] Torus Insurance Holdings Limited [Member] Trident [Member]	May 08, 2014 Bayshore [Member] Subsequent Event [Member]	May 08, 2014 Bayshore [Member] Subsequent Event [Member] Trident [Member]	May 08, 2014 Bayshore [Member] Subsequent Event [Member] Dowling [Member]	Mar. 31, 2014 Bayshore [Member] Share Capital - Ordinary Shares [Member] Torus Insurance Holdings Limited [Member]	May 08, 2014 Bayshore [Member] Kenmare [Member] Subsequent Event [Member]	Mar. 31, 2014 Northshore [Member] Trident [Member]	May 08, 2014 Northshore [Member] Subsequent Event [Member]	May 08, 2014 Northshore [Member] Subsequent Event [Member] Trident [Member]	Apr. 17, 2014 Northshore [Member] Subsequent Event [Member] Trident [Member]	May 08, 2014 Northshore [Member] Subsequent Event [Member] Atrium [Member]	Apr. 17, 2014 Northshore [Member] Subsequent Event [Member] Atrium [Member]	May 08, 2014 Northshore [Member] Subsequent Event [Member] Dowling [Member]	May 08, 2014 Northshore [Member] Kenmare [Member] Subsequent Event [Member]	Apr. 17, 2014 Northshore [Member] Kenmare [Member] Subsequent Event [Member]
Business Acquisition [Line Items]
Percentage of interest directly owned				40.00%										60.00%
Purchase price for amalgamation							$ 646.0
Common shares, par value		$ 1	$ 1				$ 132					$ 1.00
Amalgamation agreement date		Jul. 08, 2013
Average closing price of voting ordinary shares prior to trading period																							20 days
Company contributed purchase price	41.6
Acquisition purchase price	3.6	397.7		258.4
Ordinary shares, shares issued		1,501,211					1,898,326	397,115		13,846,728	13,802,706
Preferred shares issued		714,015											714,015
Cash contribution		$ 136
Related transaction expenses		2.4
Ownership percentage of ordinary shares							9.50%
Ownership percentage of outstanding share capital							11.50%
Interest owned by an entity									40.00%							60.00%
Shares vesting period					2 years	3 years
Interest owned by employees																											38.10%	38.10%	4.80%	4.80%		57.70%	57.10%
Investment in entities																				$ 15.4						$ 15.4
Ownership percentage																					40.00%			60.00%
Interest owned by co-investor																					39.30%	1.70%		59.00%			37.40%		4.80%		1.70%	56.10%
Shareholders agreement period		90 days		90 days													5 years
Interest owned by an entity															55.00%			40.00%	100.00%						40.00%