Consolidated Statements of Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of shares of common stock issued under stock option plan	104,277	167,675	45,289
Number of common stock shares purchased	76,790	43,835	41,915
Common stock	$ 0.86	$ 0.78	$ 0.73
Common Stock [Member]
Number of shares of common stock issued under stock option plan	104,277	167,675	45,289
Additional Paid-in Capital [Member]
Number of shares of common stock issued under stock option plan	104,277	167,675	45,289
Treasury Stock [Member]
Number of common stock shares purchased	76,790	43,835	41,915