Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Allowance for uncollectible accounts	$ 190	$ 200
Capitalization:
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	36,000,000	36,000,000
Common stock, shares issued	20,520,856	20,456,225
Common stock, shares outstanding	20,520,856	20,456,225