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CAPITAL STOCK, Employee Stock Purchase Plan (Details) - $ / shares
3 Months Ended 12 Months Ended
Jun. 30, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Jun. 30, 2017
Nov. 30, 2014
Jun. 30, 2008
Mar. 31, 2008
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized 3,000,000 8,040,000.00     1,290,000.00 3,750,000.00 2,500,000 1,700,000
Employee Stock Purchase Plan Description   Our Second Amended and Restated ESPP offers our shares for purchase at a price equal to 85% of the closing price on the applicable offering period termination date. Shares issued under the ESPP are considered compensatory. Accordingly, we are required to measure fair value and record compensation expense for share purchase rights granted under the ESPP. In July 2015, the Board of Directors approved an amendment to the ESPP to change the subscription period from three to six months and accordingly to adjust the payroll cap to $5,000 per plan period.            
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant   2,978,714            
Weighted-average assumptions and fair value of shares issued under the ESPP                
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized 650,000              
Employee Stock Purchase Plan [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant   650,111            
Weighted-average assumptions and fair value of shares issued under the ESPP                
Expected dividend yield (in hundredths)   0.00% 0.00% 0.00%        
Risk-free interest rate (in hundredths)   1.85% 0.83% 0.40%        
Expected volatility (in hundredths)   55.30% 62.00% 69.00%        
Expected life (in years)   182 days 179 days 179 days        
Weighted-average fair value of shares issued (in dollars per share)   $ 0.94 $ 0.86 $ 1.20        
Shares issued under the ESPP (in shares)   117,653 96,507 129,342        
Average price of shares issued (in dollars per share)   $ 4.22 $ 4.53 $ 4.35