| UNAUDITED QUARTERLY FINANCIAL INFORMATION | 20.  UNAUDITED QUARTERLY FINANCIAL INFORMATION Quarterly Results of Operations  
|   |   | For the quarter ended |   |  
|   |   | Dec 28, |   |   | Sept 28, |   |   | Jun 29, |   |   | Mar 30, |   |  
|   |   | 2019 |   |   | 2019 |   |   | 2019 |   |   | 2019 |   |  
| Net sales |   | $ | 125,927 |   |   | $ | 138,045 |   |   | $ | 143,842 |   |   | $ | 146,851 |   |  
| Gross profit |   |   | 47,427 |   |   |   | 52,119 |   |   |   | 56,227 |   |   |   | 56,509 |   |  
| Operating income |   |   | 18,772 |   |   |   | 19,138 |   |   |   | 26,373 |   |   |   | 25,832 |   |  
| Income before income taxes |   |   | 16,861 |   |   |   | 15,462 |   |   |   | 21,925 |   |   |   | 21,059 |   |  
| Net income |   |   | 13,809 |   |   |   | 12,791 |   |   |   | 17,265 |   |   |   | 16,404 |   |  
| Basic and diluted net income per common share |   | $ | 0.43 |   |   | $ | 0.40 |   |   | $ | 0.54 |   |   | $ | 0.51 |   |    
|   |   | For the quarter ended |   |  
|   |   | Dec 29, |   |   | Sept 29, |   |   | Jun 30, |   |   | Mar 31, |   |  
|   |   | 2018 |   |   | 2018 |   |   | 2018 |   |   | 2018 |   |  
| Net sales |   | $ | 138,722 |   |   | $ | 135,837 |   |   | $ | 136,168 |   |   | $ | 97,318 |   |  
| Gross profit |   |   | 52,927 |   |   |   | 51,735 |   |   |   | 50,404 |   |   |   | 37,617 |   |  
| Operating income |   |   | 22,052 |   |   |   | 19,246 |   |   |   | 17,003 |   |   |   | 17,253 |   |  
| Income before income taxes |   |   | 17,032 |   |   |   | 14,250 |   |   |   | 9,220 |   |   |   | 15,893 |   |  
| Net income |   |   | 16,424 |   |   |   | 11,599 |   |   |   | 6,796 |   |   |   | 11,911 |   |  
| Basic and diluted net income per common share |   | $ | 0.51 |   |   | $ | 0.36 |   |   | $ | 0.22 |   |   | $ | 0.40 |   |  |