Share Capital - Changes in Number of Shares of Class A Stock Outstanding (Details) (Class A Stock [Member])	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Oct. 07, 2011
Class A Stock [Member]
Class of Stock [Line Items]
Class A Stock outstanding, beginning of year	13,530,688	13,377,967	13,572,265
Issued pursuant to shared-based compensation plans	104,143	138,659
Class A Stock outstanding, end of year	13,634,831	13,516,626	13,572,265