Share Capital - Changes in Number of Shares of Class A Stock Outstanding (Detail) (Class A Stock [Member])	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Mar. 31, 2014	Mar. 31, 2013	Oct. 07, 2011
Class A Stock [Member]
Class of Stock [Line Items]
Class A Stock outstanding, beginning of year			13,377,967	13,508,318	13,519,126	13,496,783	13,572,265
Issued pursuant to shared-based compensation plans	11,562	65,227	152,721	65,227
Class A Stock outstanding, end of year	13,530,688	13,442,759	13,530,688	13,442,759	13,519,126	13,496,783	13,572,265
Stock Repurchased and Retired During Period, Shares		(119,251)		(130,786)