Condensed Financial Information - Balance Sheets (Parenthetical) (Detail) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements Captions [Line Items]
Preferred Stock, par value	$ 0.10	$ 0.10
Preferred Stock, authorized shares	1,000,000	1,000,000
Preferred Stock, issued shares	0	0
Common Stock, par value	$ 0.10	$ 0.10
Common Stock, authorized shares	50,000,000	50,000,000
Common Stock, issued shares	36,530,000	36,147,000
Parent Company
Condensed Financial Statements Captions [Line Items]
Preferred Stock, par value	$ 0.10	$ 0.10
Preferred Stock, authorized shares	1,000,000	1,000,000
Preferred Stock, issued shares	0	0
Common Stock, par value	$ 0.10	$ 0.10
Common Stock, authorized shares	50,000,000	50,000,000
Common Stock, issued shares	36,530,000	36,147,000
Treasury Stock, shares	7,023,000	7,023,000