Consolidated Condensed Statement of Equity (Parenthetical) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidated Condensed Statement of Equity [Abstract]
Restricted stock issuances (in shares)	211,328	200,688	110,825
Stock repurchase (in shares)		2,250,236	1,752,454
Stock options exercised (in shares)		77,334	27,619
Conversion of Class B shares	31,800
Common Stock, Dividends, Per Share, Cash Paid	$ 0.0675	$ 0.2550	$ 0.2500