Common Shares (Details) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Common Shares (Textual) [Abstract]
Vested options exercised by employees , shares	1.0	0.8
Proceeds from issuance of common shares	$ 15,700,000	$ 9,424,000
Cash outflow from issuance of common shares	21,000,000
Common shares withheld by company	0.1	0.1
Common shares fair value	1,800,000	2,300,000
Provision for contingent liability			$ 100,000,000