Note 4 - Stock-based Compensation  | 
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| Notes to Financial Statements | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Disclosure of Compensation Related Costs, Share-based Payments [Text Block] | 
 Note  4.  Stock-Based CompensationThe Company recorded   $590,419  and $1,774,330  of compensation expense related to current and past option grants, restricted stock grants and the Company’s Employee Stock Purchase Plan (“ESPP”) for the three  and nine  months ended  June 30, 2017,  respectively. For the three  months ended  June 30, 2017,  
$535,719  of this expense is included in selling, general and administrative expense, and $54,700  is included in cost of sales. For the nine  months ended  June 30, 2017,  
$1,610,229  of this expense is included in selling, general and administrative expense, and $164,101  is included in cost of sales. The Company recorded $370,465  and $843,658  of compensation expense related to current and past equity awards for the three  and nine  months ended  June 30, 2016,  respectively. For the three  months ended  June 30, 2016,  
$336,310  of this expense was included in selling, general and administrative expense, and $34,155  was included in cost of sales. For the nine  months ended  June 30, 2016,  
$765,347  of this expense was included in selling, general and administrative expense, and $78,311  was included in cost of sales. As of  June 30, 2017,  
$5,750,033  of total unrecognized compensation expense related to non-vested restricted stock awards is expected to be recognized over a period of approximately 7.3  years.There were 
  no  nine  month periods ended  June 30, 2017  or  June 30, 2016.  The following is a summary of stock option activity during the nine  months ended  June 30, 2017: 
 The intrinsic value of an option is the amount by which the fair value of the underlying stock exceeds its exercise price. As of    June 30, 2017,  the weighted average remaining contractual term for all outstanding and exercisable stock options was 3.0  years and their aggregate intrinsic value was $405,657.  During the nine  months ended  June 30, 2017,  the Company received proceeds of $28,718  from the exercise of stock options. During the nine  months ended  June 30, 2016,  exercised stock options totaled 172,450  shares, resulting in $473,651  of proceeds to the Company.Restricted Stock The Company’s   2007  Stock Compensation Plan permits its Compensation Committee to grant stock-based awards, including stock options and restricted stock, to key employees and non-employee directors. The Company has made restricted stock grants that vest over one  to ten  years.During the   nine  month period ended  June 30, 2017,  the Company granted non-employee directors restricted stock awards totaling 3,795  shares of common stock, with a vesting term of approximately one  year and a fair value of $16.45  per share.During the   nine  month period ended  June 30, 2016,  the Company granted non-employee directors restricted stock awards totaling 2,712  shares of common stock, with a vesting term of approximately one  year and a fair value of $14.73  per share. The Company also granted outgoing non-employee directors fully-vested stock awards totaling 1,356  shares of common stock, with a fair value of $14.73  per share. Additionally, the Company granted employees restricted stock awards totaling 259,555  shares of common stock, with a vesting term of three  to five  years and a fair value of $17.43  per share during the nine  month period ended  June 30, 2016. 
Restricted stock transactions during the   nine  month period ended  June 30, 2017  are summarized as follows:
 Employee Stock Purchase Plan  Clearfield, Inc.’s ESPP allows participating employees to purchase shares of the Company’s common stock at a discount through payroll deductions. The ESPP is available to all employees subject to certain eligibility requirements. Terms of the ESPP provide that participating employees  
 may  purchase the Company’s common stock on a voluntary after-tax basis. Employees  may  purchase the Company’s common stock at a price that is no  less than the lower of 85%  of the fair market value of one  share of common stock at the beginning or end of each stock purchase period or phase. The ESPP is carried out in six  month phases, with phases beginning on  January 1  and  July 1  of each calendar year. For the phases that ended on  June 30, 2017  and  December 31, 2016,  employees purchased 14,723  and 11,144  shares at a price of $11.22  and $15.21  per share, respectively. After the employee purchase on  June 30, 2017,  
117,255  shares of common stock were available for future purchase under the ESPP. | 
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