CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($)
shares in Thousands, $ in Thousands
Total
Common Stock
Additional Paid-in Capital
Accumulated Other Comprehensive Loss
Accumulated Deficit
Treasury Stock
Beginning Balance, shares at Dec. 31, 2018   53,955        
Balance at beginning of period at Dec. 31, 2018 $ 151,934 $ 1,482 $ 876,073 $ (753) $ (684,882) $ (39,986)
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Stock-based compensation 5,714   5,714      
Exercise of stock options, shares   55        
Exercise of stock options 326 $ 2 324      
Issuance of vested restricted stock units (in shares)   501        
Issuance of vested restricted stock units (156) $ 13 (169)      
Stock issued under employee stock purchase plans (in shares)   932        
Stock issued under employee stock purchase plans 4,157 $ 23 4,134      
Net loss (14,812)       (14,812)  
Other comprehensive income (loss) 43     43    
Ending Balance, shares at Jun. 29, 2019   55,443        
Balance at end of period at Jun. 29, 2019 147,206 $ 1,520 886,076 (710) (699,694) (39,986)
Beginning Balance, shares at Mar. 30, 2019   54,164        
Balance at beginning of period at Mar. 30, 2019 145,841 $ 1,488 879,475 (487) (694,649) (39,986)
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Stock-based compensation 2,569   2,569      
Exercise of stock options, shares   6        
Exercise of stock options 35 $ 0 35      
Issuance of vested restricted stock units (in shares)   334        
Issuance of vested restricted stock units (130) $ 8 (138)      
Stock issued under employee stock purchase plans (in shares)   939        
Stock issued under employee stock purchase plans 4,159 $ 24 4,135      
Net loss (5,045)       (5,045)  
Other comprehensive income (loss) (223)     (223)    
Ending Balance, shares at Jun. 29, 2019   55,443        
Balance at end of period at Jun. 29, 2019 $ 147,206 $ 1,520 886,076 (710) (699,694) (39,986)
Beginning Balance, shares at Dec. 31, 2019 56,448 56,448        
Balance at beginning of period at Dec. 31, 2019 $ 154,028 $ 1,545 895,899 (854) (702,576) (39,986)
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Stock-based compensation $ 6,225   6,225      
Exercise of stock options, shares 700 748        
Exercise of stock options $ 5,608 $ 19 5,589      
Issuance of vested restricted stock units (in shares)   280        
Issuance of vested restricted stock units 0 $ 7 (7)      
Stock issued under employee stock purchase plans (in shares)   667        
Stock issued under employee stock purchase plans 4,712 $ 16 4,696      
Net loss (11,156)       (11,156)  
Other comprehensive income (loss) $ (249)     (249)    
Ending Balance, shares at Jun. 27, 2020 58,143 58,143        
Balance at end of period at Jun. 27, 2020 $ 159,168 $ 1,587 912,402 (1,103) (713,732) (39,986)
Beginning Balance, shares at Mar. 28, 2020   56,628        
Balance at beginning of period at Mar. 28, 2020 150,915 $ 1,549 899,978 (1,106) (709,520) (39,986)
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Stock-based compensation $ 3,241   3,241      
Exercise of stock options, shares 600 591        
Exercise of stock options $ 4,509 $ 15 4,494      
Issuance of vested restricted stock units (in shares)   233        
Issuance of vested restricted stock units 0 $ 6 (6)      
Stock issued under employee stock purchase plans (in shares)   691        
Stock issued under employee stock purchase plans 4,712 $ 17 4,695      
Net loss (4,212)       (4,212)  
Other comprehensive income (loss) $ 3     3    
Ending Balance, shares at Jun. 27, 2020 58,143 58,143        
Balance at end of period at Jun. 27, 2020 $ 159,168 $ 1,587 $ 912,402 $ (1,103) $ (713,732) $ (39,986)