| Reconciliation of Revenue from Segments to Consolidated [Table Text Block] | 
		
			|  |  | Year ended September 30, 2023 |  |  
			| (in thousands) |  | Clearfield |  |  | Nestor Cables |  |  | Eliminations |  |  | Consolidated |  |  
			| Revenue from external customers |  | $ | 225,722 |  |  | $ | 42,998 |  |  | $ | - |  |  | $ | 268,720 |  |  
			| Revenue from internal customers (Clearfield) |  |  | - |  |  |  | 5,408 |  |  |  | (5,408 | ) |  |  | - |  |  
			| Net investment income |  |  | 5,315 |  |  |  | 7 |  |  |  | (116 | ) |  |  | 5,206 |  |  
			| Interest Expense |  |  | 170 |  |  |  | 827 |  |  |  | (116 | ) |  |  | 881 |  |  
			| Depreciation and amortization |  |  | 4.598 |  |  |  | 1,456 |  |  |  | - |  |  |  | 6,054 |  |  
			| Stock based compensation |  |  | 3,528 |  |  |  | 50 |  |  |  | - |  |  |  | 3,578 |  |  
			| Income taxes |  |  | 8,883 |  |  |  | 196 |  |  |  | - |  |  |  | 9,079 |  |  
			| Net Income |  |  | 32,834 |  |  |  | 719 |  |  |  | (1,020 | ) |  |  | 32,533 |  |  
			| Capital Expenditures |  |  | 6,759 |  |  |  | 925 |  |  |  | - |  |  |  | 7,684 |  |  
		
			|  |  | Year ended September 30, 2022 |  |  
			| (in thousands) |  | Clearfield |  |  | Nestor Cables |  |  | Eliminations |  |  | Consolidated |  |  
			| Revenue from external customers |  | $ | 263,822 |  |  | $ | 7,061 |  |  | $ | - |  |  | $ | 270,883 |  |  
			| Revenue from internal customers (Clearfield) |  |  | - |  |  |  | 182 |  |  |  | (182 | ) |  |  | - |  |  
			| Net investment income |  |  | 327 |  |  |  | 1 |  |  |  | - |  |  |  | 328 |  |  
			| Interest Expense |  |  | 141 |  |  |  | 170 |  |  |  | - |  |  |  | 311 |  |  
			| Depreciation and amortization |  |  | 3,187 |  |  |  | 239 |  |  |  | - |  |  |  | 3,426 |  |  
			| Stock based compensation |  |  | 2,339 |  |  |  | - |  |  |  | - |  |  |  | 2,339 |  |  
			| Income taxes |  |  | 14,258 |  |  |  | 214 |  |  |  | - |  |  |  | 14,472 |  |  
			| Net Income (loss) |  |  | 49,771 |  |  |  | (389 | ) |  |  | (20 | ) |  |  | 49,362 |  |  
			| Capital Expenditures |  |  | 8,487 |  |  |  | 13 |  |  |  | - |  |  |  | 8,500 |  |  | 
| Reconciliation of Assets from Segment to Consolidated [Table Text Block] | 
		
			|  |  | Year ended September 30, 2023 |  |  
			| (in thousands) |  | Clearfield |  |  | Nestor Cables |  |  | Eliminations |  |  | Consolidated |  |  
			| Goodwill |  | $ | 4,709 |  |  | $ | 1,819 |  |  | $ | - |  |  | $ | 6,528 |  |  
			| Total assets |  | $ | 335,412 |  |  | $ | 43,550 |  |  | $ | (23,445 | ) |  | $ | 355,517 |  |  
		
			|  |  | Year ended 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 |  |  |