Segment Information - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 Segment	Mar. 31, 2013
Segment Reporting Information [Line Items]
Number of underwriting segments	2
Combined ratio indicating underwriting profit	100.00%
Combined ratio indicating underwriting loss	100.00%
Net earned premiums	$ 225,272	$ 202,328
Insurance Companies
Segment Reporting Information [Line Items]
Net earned premiums	165,884	154,331
Insurance Companies | UK Branch
Segment Reporting Information [Line Items]
Net earned premiums	$ 11,600	$ 10,100