Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss)
As at	$ 60.3
Current period change	26.6
As at	86.9
Foreign currency translation adjustment
Accumulated Other Comprehensive Income (Loss)
As at	61.4
Current period change	23.7
As at	85.1
Unrealized holding gain/(loss) on available-for-sale securities
Accumulated Other Comprehensive Income (Loss)
As at	(1.1)
Current period change	2.9
As at	$ 1.8