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Stockholders' Equity and Employee Stock Option Plans 1997 Stock Plan (Details) - shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Apr. 01, 2013
Mar. 31, 2013
Equity [Abstract]          
Common Stock, Capital Shares Reserved for Future Issuance       1,090,540 2,097,283
Options and SARS, Outstanding, Number 425,722 505,872 285,536   550,540
Share-based Compensation Arrangement by Share-based Payment Award, Additional Shares Authorized in 2013 Amendment       540,000  
New plan shares approved, Shares   750,000      
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant 333,982 602,825 517,505   1,546,743
Restricted Stock [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Award vesting period (in years) 4 years        
2016 Equity Incentive Plan [Member]          
Equity [Abstract]          
Common Stock, Capital Shares Reserved for Future Issuance 1,100,000        
Options and SARS, Outstanding, Number 892,629        
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant 187,982        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Purchase price as a percent of fair market value 100.00%        
Purchase price as a percent of fair market value for owners of more than 10% of stock 110.00%        
1997 Stock Plan [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Purchase price as a percent of fair market value 100.00%        
Award vesting period (in years) 4 years        
1997 Stock Plan [Member] | Restricted Stock [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Award expiration term (in years) 5 years        
Award vesting period (in years) 4 years        
1997 Stock Plan [Member] | Stock Appreciation Rights (SARs) [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Purchase price as a percent of fair market value 100.00%        
Award expiration term (in years) 5 years        
Award vesting period (in years) 4 years