Common Shares (Details) (USD $)	0 Months Ended		9 Months Ended
	Sep. 11, 2014	Jul. 24, 2014	Sep. 30, 2014	Sep. 30, 2013	Sep. 11, 2014
Common shares
Issuance of common shares for stock options exercised (in shares)			3,000,000	500,000
Proceeds from stock options exercised			$ 30,200,000	$ 4,400,000
Common shares withheld by company			300,000	200,000
Common shares fair value			7,600,000	3,100,000
Common stock dividend declared (in dollars per share)		$ 0.06
Cash dividends paid			41,781,000	35,357,000
Shares purchased	10,375,000
Share price of shares purchased (in dollars per share)					$ 24.10
Total aggregate amount of shares purchased	$ 250,000,000