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Stockholders' Equity (ESPP) (Details) - USD ($)
$ in Thousands
3 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Risk-free interest rate         1.44%
Forecast          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Risk-free interest rate 1.83% 1.72% 1.61%    
ESPP          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Share-based compensation expense       $ 97 $ 96
Dividend yield       0.01%  
Expected volatility       20.89%  
Expected holding period (years)         3 months
ESPP | Forecast          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Expected holding period (years) 1 year 9 months 6 months