Capital Stock (Details) - USD ($)		1 Months Ended	9 Months Ended	117 Months Ended
	Jun. 30, 2016	Apr. 30, 2016	Aug. 31, 2016	Aug. 31, 2016
Equity, Class of Treasury Stock [Line Items]
Stock repurchased during the period			$ 37,970,000
Annual dividend approved (in dollars per share)		$ 0.41
Dividends paid	$ 18,900,000
Class A Common Stock | Stock Purchase Plan [Member]
Equity, Class of Treasury Stock [Line Items]
Authorized amount under Stock Purchase Plan			$ 330,000,000	$ 330,000,000
Stock repurchased during the period (shares)			1,098,525	8,162,487
Stock repurchased during the period			$ 37,400,000	$ 305,700,000
Weighted average price of stock repurchased (in US$ per share)			$ 34.04
Remaining repurchase authority under the Stock Purchase Plan			$ 24,300,000	$ 24,300,000