Condensed Consolidated Statements of Stockholders' Equity (Parenthetical) - shares	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Statement of Stockholders' Equity [Abstract]
Stock issued for benefit plans	0	0
Options exercised	29,199	0
Purchase of treasury stock (shares)	15,107	28,279
Employee stock purchase plan	0	0
Issuance of restricted stock (shares)	107,388	141,818
Issuance of common stock (shares)	0	1,403,508