Treasury Stock - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Equity, Class of Treasury Stock [Line Items]
Treasury stock, shares repurchased value	$ 48,244,000	$ 110,977,000
Treasury stock, shares	7,648,000	7,285,000
Treasury stock, cost	$ 634,405,000	$ 586,161,000
Class A
Equity, Class of Treasury Stock [Line Items]
Treasury stock, shares repurchased	0	0
Treasury stock, shares repurchased value	$ 0	$ 0
Class A | Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Shares repurchased program expiration date	Apr. 29, 2023
Stock authorized to repurchase by board of directors	$ 800,000,000
Treasury stock, shares repurchased	362,148		0
Shares repurchased, average price per share	$ 133.21
Treasury stock, shares repurchased value	$ 48,200,000
Treasury stock, shares	5,069,762
Shares repurchased, average price per share	$ 99.51
Treasury stock, cost	$ 504,500,000