XML 37 R127.htm IDEA: XBRL DOCUMENT v2.4.0.8
Employee Share-Based Incentive Compensation Plans (WTM Performance Shares) (Details) (USD $)
 12 Months Ended 12 Months Ended
Dec. 31, 2013
One Beacon Employee Stock Ownership Plan
Dec. 31, 2013
Performance Shares [Member]
White Mountains
multiplier
Dec. 31, 2013
Performance Shares [Member]
W T M Incentive and Phantom Plan [Member]
Dec. 31, 2012
Performance Cycle From 2010 to 2012
W T M Incentive and Phantom Plan [Member]
Dec. 31, 2013
W T M Incentive and Phantom Plan [Member]
Performance Shares [Member]
Dec. 31, 2013
Performance Cycle From 2010 to 2012
Performance Shares [Member]
W T M Incentive and Phantom Plan [Member]
Dec. 31, 2012
Performance Cycle From 2009 to 2011
Performance Shares [Member]
Dec. 31, 2012
Performance Cycle From 2009 to 2011
Performance Shares [Member]
W T M Incentive and Phantom Plan [Member]
Dec. 31, 2013
IRS
OneBeacon
Share-based compensation arrangement by share-based payment award                  
Vesting period (in years)         3 years        
Annual base contribution provided to participants expressed as percentage of salary 3.00%                
Social security wage base amount maximum $ 113,700                
Variable contribution provided to participants (as percentage) 6.00%                
Deferred Benefit Plan Compensation Limits                 255,000
Multiplier for determining payout, low end of range   0              
Multiplier for determining payout, high end of range   2              
Performance cycle period   3 years              
Performance goal percentage for minimum payout           33.00%   147.00%  
Payout for maximum growth target percentage           98.00%   155.00%  
Partial Payout for 2010 - 2012 cycle       9.9          
Vested (in shares)             9,577    
Unamortized grant date fair value     $ 33,800,000