Schedule I - Parent Company Financial Information (Condensed Balance Sheets) (Parenthetical) (Detail) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Preferred stock, par	$ 1	$ 1
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, issued	0	0
Common stock, par	$ 0.1667	$ 0.1667
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	198,372,059	197,951,551
Treasury stock, shares	50,084,043	48,347,541
Parent Company
Condensed Financial Statements, Captions [Line Items]
Preferred stock, par	$ 1	$ 1
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, issued	0	0
Common stock, par	$ 0.1667	$ 0.1667
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	198,372,059	197,951,551
Treasury stock, shares	50,084,043	48,347,541