Treasury Stock - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Equity, Class of Treasury Stock [Line Items]
Treasury stock, shares	6,405,000		6,405,000		6,405,000
Treasury stock, cost	$ 475,184,000		$ 475,184,000		$ 475,184,000
Class A | 2005 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Shares repurchased program expiration date			Apr. 29, 2018
Stock authorized to repurchase by board of directors	$ 800,000,000		$ 800,000,000
Treasury stock, shares	3,826,947		3,826,947
Treasury stock, shares repurchased	0	0	0	0
Shares repurchased, average price per share			$ 90.23
Treasury stock, cost	$ 345,300,000		$ 345,300,000