Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts receivable:
Allowance for doubtful accounts	$ 39	$ 22
Shareholders’ equity:
Preferred stock, par value (in usd per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	5,882,000	5,882,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in usd per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	50,000,000	50,000,000
Common stock, shares issued (in shares)	34,062,000	33,938,000
Common stock, shares outstanding (in shares)	27,152,000	27,028,000
Treasury stock, shares held (in shares)	6,910,000	6,910,000