Components Of Equity - Additional Information (Detail) - $ / shares shares in Thousands				9 Months Ended
	Nov. 05, 2018	May 08, 2018	May 02, 2017	Sep. 30, 2018	Sep. 30, 2017
Class of Stock [Line Items]
Date of declaration of dividends		May 08, 2018	May 02, 2017
Dividend declared per share		$ 0.45	$ 0.42
Date of dividend payment		Jun. 15, 2018	Jun. 15, 2017
Dividends payable to shareholders date of record		Jun. 01, 2018	Jun. 01, 2017
Non-Discretionary Plan
Class of Stock [Line Items]
Shares repurchased				2,386	2,902
Average price per share				$ 72.72	$ 55.58
Discretionary Plan
Class of Stock [Line Items]
Shares repurchased				5,378	3,189
Average price per share				$ 71.07	$ 56.26
Expected common stock shares issued and outstanding				170,000
Subsequent Event
Class of Stock [Line Items]
Date of declaration of dividends	Nov. 05, 2018
Dividend declared per share	$ 0.45
Date of dividend payment	Dec. 17, 2018
Dividends payable to shareholders date of record	Dec. 03, 2018
Subsequent Event | Discretionary Plan
Class of Stock [Line Items]
Expected common stock shares issued and outstanding	160,000