Common Shares (Details) (USD $)	0 Months Ended		3 Months Ended
	Mar. 28, 2013	Feb. 27, 2013	Mar. 31, 2013	Mar. 31, 2012
Common shares
Vested options exercised by employees, shares			100,000	1,000,000
Proceeds from stock options exercised			$ 1,000,000	$ 15,700,000
Repurchase surrendered unexercised vested options surrendered to satisfy exercise price and related tax withholding obligations			21,000,000
Common shares withheld by company			200,000	100,000
Common shares fair value			2,800,000	1,800,000
Dividend declared (in dollars per share)		$ 0.04
Dividend paid	$ 12,900,000		$ 12,891,000