Components Of Equity - Additional Information (Detail) - $ / shares shares in Thousands		3 Months Ended
	May 08, 2018	Mar. 31, 2018	Mar. 31, 2017
Non-Discretionary Plan
Class of Stock [Line Items]
Shares repurchased		445	954
Average price per share		$ 65.68	$ 56.49
Discretionary Plan
Class of Stock [Line Items]
Shares repurchased		2,216	0
Average price per share		$ 64.58
Expected common stock shares issued and outstanding		170,000
Subsequent Event
Class of Stock [Line Items]
Date of declaration of dividends	May 08, 2018
Dividend declared per share	$ 0.45
Date of dividend payment	Jun. 15, 2018
Dividends payable to shareholders date of record	Jun. 01, 2018