| Reconciliation of Revenue from Segments to Consolidated [Table Text Block] | 
		
			|  |  | Three months ended March 31, 2023 |  |  
			| (In thousands) |  | Clearfield |  |  | Nestor Cables |  |  | Eliminations |  |  | Consolidated |  |  
			| Revenue from external customers |  | $ | 60,451 |  |  | $ | 11,358 |  |  | $ | - |  |  | $ | 71,809 |  |  
			| Revenue from internal customers (Clearfield, Inc.) |  |  | - |  |  |  | 1,737 |  |  |  | (1,737 | ) |  |  | - |  |  
			| Net investment income |  |  | 1,394 |  |  |  | 1 |  |  |  | - |  |  |  | 1,395 |  |  
			| Interest expense |  |  | - |  |  |  | 112 |  |  |  | - |  |  |  | 112 |  |  
			| Depreciation and amortization |  |  | 1,099 |  |  |  | 359 |  |  |  | - |  |  |  | 1,458 |  |  
			| Stock based compensation |  |  | 784 |  |  |  | - |  |  |  | - |  |  |  | 784 |  |  
			| Income taxes |  |  | 2,873 |  |  |  | 101 |  |  |  | - |  |  |  | 2,974 |  |  
			| Net income (loss) |  |  | 10,395 |  |  |  | 402 |  |  |  | (433 | ) |  |  | 10,364 |  |  
			| Capital expenditures |  |  | 2,481 |  |  |  | 98 |  |  |  | - |  |  |  | 2,579 |  |  
		
			|  |  | Six months ended March 31, 2023 |  |  
			| (In thousands) |  | Clearfield |  |  | Nestor Cables |  |  | Eliminations |  |  | Consolidated |  |  
			| Revenue from external customers |  | $ | 138,806 |  |  | $ | 18,945 |  |  | $ | - |  |  | $ | 157,751 |  |  
			| Revenue from internal customers (Clearfield, Inc.) |  |  | - |  |  |  | 2,923 |  |  |  | (2,923 | ) |  |  | - |  |  
			| Net investment income |  |  | 1,694 |  |  |  | 4 |  |  |  | - |  |  |  | 1,698 |  |  
			| Interest expense |  |  | 170 |  |  |  | 186 |  |  |  | - |  |  |  | 356 |  |  
			| Depreciation and amortization |  |  | 2,110 |  |  |  | 712 |  |  |  | - |  |  |  | 2,822 |  |  
			| Stock based compensation |  |  | 1,444 |  |  |  | - |  |  |  | - |  |  |  | 1,444 |  |  
			| Income taxes |  |  | 6,646 |  |  |  | 23 |  |  |  | - |  |  |  | 6,669 |  |  
			| Net income (loss) |  |  | 25,113 |  |  |  | 92 |  |  |  | (586 | ) |  |  | 24,619 |  |  
			| Capital expenditures |  |  | 4,490 |  |  |  | 308 |  |  |  | - |  |  |  | 4,798 |  |  | 
| Reconciliation of Assets from Segment to Consolidated [Table Text Block] | 
		
			|  |  | March 31, 2023 |  |  
			| (In thousands) |  | Clearfield |  |  | Nestor Cables |  |  | Eliminations |  |  | Consolidated |  |  
			| Goodwill |  | $ | 4,709 |  |  | $ | 1,878 |  |  | $ | - |  |  | $ | 6,587 |  |  
			| Total assets |  |  | 332,906 |  |  |  | 43,135 |  |  |  | (18,646 | ) |  |  | 357,395 |  |  
		
			|  |  | September 30, 2022 |  |  
			| (In thousands) |  | Clearfield |  |  | Nestor Cables |  |  | Eliminations |  |  | Consolidated |  |  
			| Goodwill |  | $ | 4,709 |  |  | $ | 1,693 |  |  | $ | - |  |  | $ | 6,402 |  |  
			| Total assets |  |  | 214,785 |  |  |  | 31,023 |  |  |  | (16,680 | ) |  |  | 229,128 |  |  |