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Stockholders' Equity (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated Share-based Compensation Expense $ 3,518 $ 3,651 $ 3,734
Stock-based compensation awards excluding ESPP [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated Share-based Compensation Expense 3,468 3,640  
Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated Share-based Compensation Expense 2,760 2,938 2,422
Stock options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated Share-based Compensation Expense $ 707 $ 702 $ 1,229
Schedule of weighted-average assumptions used to value options as of their grant date      
Risk-free interest rate 1.98% 1.43% 1.55%
Expected volatility 35.70% 38.20% 43.30%
Expected life (in years) 4 years 2 months 19 days 4 years 2 months 4 days 4 years 2 months 1 day
Dividend yield 0.00% 0.00% 0.00%