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Description of Business and Summary of Significant Accounting Policies (Narrative) (Details) - USD ($)
shares in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Description Of Business And Significant Accounting Policies [Line Items]      
Shipping and handling revenue $ 1,090 $ 1,266 $ 1,056
Payment terms for end-users 30 days    
Payment terms for distributors 60 days    
Depreciation $ 7,761 7,655 4,975
Net carrying amount of loaned equipment $ 28,749 $ 29,995  
Company's expense related to the medical device excise tax     $ 667
Options, restricted stock and performance based shares excluded from calculation of net loss per share 4,321 4,320 4,255
Advertising costs $ 900 $ 625 $ 476
Share-based compensation expense recognized $ 14,615 $ 11,697 $ 8,997
Maximum [Member]      
Description Of Business And Significant Accounting Policies [Line Items]      
Maturity period of short term investment 1 year