Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Accounts receivable, allowance for doubtful accounts	$ 507	$ 431
Stockholders' equity:
Preferred stock, par value (in dollars per share)	$ 25	$ 25
Preferred stock, shares authorized (in shares)	2,000,000	2,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0667	$ 0.0667
Common stock, shares authorized (in shares)	120,000,000	120,000,000
Common stock, shares issued (in shares)	32,213,094	32,019,605
Common stock, shares outstanding (in shares)	32,208,686	32,019,605
Treasury stock, shares (in shares)	4,408	0