| 
           Segment Reporting (Details) (USD $) 
        In Thousands, unless otherwise specified  | 
        3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
| 
           Jun. 30, 2012 
         | 
        
           Jul. 02, 2011 
         | 
        
           Jun. 30, 2012 
         | 
        
           Jul. 02, 2011 
         | 
      |
| Schedule of segment information | ||||
| Sales to unaffiliated customers | $ 57,031 | $ 54,770 | $ 112,305 | $ 105,473 | 
| Intercompany sales | ||||
| Operating income | 16,464 | 15,384 | 31,728 | 29,294 | 
| Depreciation | 1,634 | 1,655 | 3,286 | 3,313 | 
| Capital expenditures | 2,966 | 1,699 | 4,752 | 2,810 | 
| 
           United States [Member] 
         | 
        ||||
| Schedule of segment information | ||||
| Sales to unaffiliated customers | 39,458 | 35,152 | 75,078 | 65,618 | 
| Intercompany sales | 8,466 | 8,470 | 17,541 | 17,959 | 
| Operating income | 13,116 | 11,383 | 24,897 | 21,359 | 
| Depreciation | 1,306 | 1,292 | 2,631 | 2,585 | 
| Capital expenditures | 2,621 | 1,615 | 4,214 | 2,510 | 
| 
           Korea [Member] 
         | 
        ||||
| Schedule of segment information | ||||
| Sales to unaffiliated customers | 4,953 | 5,674 | 10,906 | 11,697 | 
| Intercompany sales | ||||
| Operating income | 508 | 659 | 1,214 | 1,599 | 
| Depreciation | 31 | 29 | 57 | 54 | 
| Capital expenditures | 9 | 23 | 20 | 146 | 
| 
           Germany [Member] 
         | 
        ||||
| Schedule of segment information | ||||
| Sales to unaffiliated customers | 7,054 | 7,308 | 14,474 | 14,496 | 
| Intercompany sales | 21 | 63 | 44 | 116 | 
| Operating income | 1,647 | 1,922 | 3,192 | 3,662 | 
| Depreciation | 78 | 88 | 160 | 188 | 
| Capital expenditures | 15 | 5 | 32 | 50 | 
| 
           United Kingdom [Member] 
         | 
        ||||
| Schedule of segment information | ||||
| Sales to unaffiliated customers | 5,566 | 6,636 | 11,847 | 13,662 | 
| Intercompany sales | 473 | 407 | 847 | 783 | 
| Operating income | 1,085 | 1,281 | 2,219 | 2,487 | 
| Depreciation | 219 | 246 | 438 | 486 | 
| Capital expenditures | 321 | 56 | 486 | 104 | 
| 
           Elimination [Member] 
         | 
        ||||
| Schedule of segment information | ||||
| Sales to unaffiliated customers | ||||
| Intercompany sales | (8,960) | (8,940) | (18,432) | (18,858) | 
| Operating income | 108 | 139 | 206 | 187 | 
| Depreciation | ||||
| Capital expenditures | ||||