Reinsurance - Additional Information (Detail) (GBP £) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Number of companies that make up reinsurance recoverable	86
Number of companies that make up majority of reinsurance recoverable	13
Percent of reinsurance recoverable made up by majority of companies	91.00%
Remaining companies rated A- or better by AM best	8.00%
Percent of recoverable held with companies less than A-	1.00%
Reinsurance Agreement [Member] | Minimum
Quota Share Reinsurance Percentage	50.00%
Quota Share Coverage Amount	£ 0.5
Reinsurance Agreement [Member] | Maximum
Quota Share Reinsurance Percentage	100.00%