Schedule I - Parent Company Financial Information (Condensed Balance Sheets) Phantom (Detail) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Preferred stock, par (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, issued (in shares)	0	0
Common stock, par (in dollars per share)	$ 0.1667	$ 0.1667
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	198,572,458	198,495,007
Treasury stock (in shares)	60,893,762	49,189,811
Parent Company
Condensed Financial Statements, Captions [Line Items]
Preferred stock, par (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, issued (in shares)	0	0
Common stock, par (in dollars per share)	$ 0.1667	$ 0.1667
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	198,572,458	198,495,007
Treasury stock (in shares)	60,893,762	49,189,811