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Share Capital - Changes in Number of Shares of Class A Stock Outstanding (Detail) (Class A Stock [Member])
 3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Oct. 07, 2011
Class A Stock [Member]
          
Class of Stock [Line Items]          
Class A Stock outstanding, beginning of period 13,508,318 13,489,162 13,508,318 13,572,265 13,572,265
Issued pursuant to shared-based compensation plans       16,797  
Repurchased and cancelled pursuant to the stock buy-back (11,535)    (11,535) (99,900)  
Class A Stock outstanding, end of period 13,496,783 13,489,162 13,496,783 13,489,162 13,572,265