Stock Repurchase Program - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 16, 2018
Equity, Class of Treasury Stock [Line Items]
Number of shares repurchased	2,750,000	3,700,000	3,833,000
Average price paid per share	$ 122.20	$ 90.90	$ 88.16
Total cost	$ 336,042	$ 336,335	$ 337,910
Remaining number of shares authorized to be repurchased under stock repurchase program	2,750,000
Subsequent Event [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, number of shares authorized to be repurchased				5,000,000