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Nature of Operations and Summary of Significant Accounting Policies - Additional Information (Detail) |  | 12 Months Ended
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Jul. 11, 2016 | Sep. 30, 2017 USD ($) Segment shares | Sep. 30, 2016 USD ($) shares | Sep. 30, 2015 USD ($) shares
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Stock split ratio |  | 1.5 |  |
Exercisable stock options, included in the diluted EPS calculation | shares |  | 463,000 | 480,000 | 0
Effect of dilutive stock options | shares |  | 284,000 | 190,000 | 0
Anti-dilutive exercisable stock options, not included in the diluted EPS calculation | shares |  | 0 | 0 | 512,000
Net unrealized gains (losses) |  | $ 1,183,000 | $ 2,502,000 | $ (4,882,000)
Transfers of investments between Level 1 and Level 2 |  | 0 | 0 |
Impairment loss recognized on an asset group |  | $ 0 | 0 | $ 0
Time for the collection of cost associated with Pre- contract |  | 1 year |  |
Valuation allowance |  | $ 0 | $ 0 |
Number of reportable segment | Segment |  | 1 |  |
Common and Class B Stock [Member] |  |  |  |
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Stock split ratio | 1.5 |  |  |
Stock dividend percentage | 50.00% |  |  |
Stock split ratio description |  | On July 11, 2016, the Company's Board of Directors approved a three-for-two split of the Company's common and Class B stock to be effected in the form of a 50% stock dividend. As a result, shareholders received one additional share of common or Class B stock for every two shares they held of the respective class of stock as of the record date. |  |
Entities Owned by One Global Company [Member] | Revenue [Member] |  |  |  |
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Percentage of concentration |  | 13.00% | 14.00% | 15.00%
Entities Owned by One Global Company [Member] | Revenue [Member] | Customer One [Member] |  |  |  |
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Percentage of concentration |  | 10.00% |  |
Entities Owned by One Global Company [Member] | Revenue [Member] | Maximum [Member] | Customer One [Member] |  |  |  |
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Percentage of concentration |  |  | 1.00% | 1.00%
Three to Four Years Old Inventory [Member] |  |  |  |
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Cost basis reduction in inventory, percentage |  | 50.00% |  |
Inventory, minimum time period on the shelf, years |  | 3 years |  |
Inventory, maximum time period on the shelf, years |  | 4 years |  |
Four to Five Years Old Inventory [Member] |  |  |  |
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Cost basis reduction in inventory, percentage |  | 75.00% |  |
Inventory, minimum time period on the shelf, years |  | 4 years |  |
Inventory, maximum time period on the shelf, years |  | 5 years |  |
Greater Than Five Years Old Inventory [Member] |  |  |  |
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items] |  |  |  |
Inventory, minimum time period on the shelf, years |  | 5 years |  |
Inventory valuation estimate |  | $ 0 |  |

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