Common Shares (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions		9 Months Ended
	Apr. 24, 2015	Sep. 30, 2015	Sep. 30, 2014
Common shares
Issuance of common shares for stock options exercised (in shares)		0.1	3.0
Proceeds from stock options exercised		$ 1,200	$ 30,200
Common shares withheld by company		0.6	0.3
Common shares fair value		$ 7,500	$ 7,600
Common stock dividend declared (in dollars per share)	$ 0.06
Cash dividends paid		$ 52,489	41,781
Shares repurchased		8.3
Total aggregate amount of shares purchased		$ 78,399	$ 250,037