Condensed Unaudited Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized	145,000,000	145,000,000
Common stock, shares issued	91,063,699	90,935,584
Treasury stock, shares	10,171,531	8,132,811
Restricted Stock Awards [Member] | Common Stock [Member]
Unvested stock awards (in shares)	1,523,484	1,421,041