Share Capital - Changes in Number of Shares of Class A Stock Outstanding (Details) - Class A Stock [Member] - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Class of Stock [Line Items]
Class A Stock outstanding, beginning of year	13,634,831	13,516,626	13,530,688	13,377,967
Issued pursuant to shared-based compensation plans	15,318	2,500	119,461	141,159
Class A Stock outstanding, end of year	13,650,149	13,519,126	13,650,149	13,519,126