Capitalized costs assets purchased

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- Definition

Contractual agreement termination date.

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- Definition

Management contract acquired.

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- Definition

Management contracts impairment amount.

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- Definition

Maximum aggregate fair market value of options granted to individual.

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- Definition

Number of mutual funds.

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- Definition

Number of open end mutual funds.

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No definition available.

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- Definition

Details of asset purchase agreement.

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No definition available.

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- Definition

Share based compensation arrangement by share based payment award exercise price percentage.

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No definition available.

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- Definition

Shareholder threshold percentage.

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No definition available.

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- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Antidilution
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Glossary Diluted Earnings Per Share
-URI http://asc.fasb.org/extlink&oid=6510752

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Name Accounting Standards Codification
-Topic 260
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-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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- Definition

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Topic 320
-SubTopic 10
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- Definition

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
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-Topic 230
-SubTopic 10
-Section 45
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-Subparagraph (b)
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- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

General descriptive information regarding an arrangement under which employees and directors receive: (a) awards of equity shares, equity share options, or other equity instruments; or (b) the entity incurs liabilities to them: (1) in amounts based, at least in part, on the price of the entity's shares or other equity instruments; or (2) that require or may require settlement by issuance of the entity's shares. Such an arrangement is usually provided to employees and directors to compensate them, provide performance incentives to them, and to attract or retain their services. May also include pertinent information particular to a plan that is not elsewhere specified in the taxonomy.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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-Paragraph 2
-Subparagraph (a)
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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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- Definition

The highest quantity of shares an employee can purchase under the plan per period.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

Maximum number of shares that may be issued in accordance with the plan as a proportion of outstanding capital stock.

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No definition available.

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Percentage of vesting of share-based compensation awards.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Summary of the Organization, Description of Business and Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Sep. 30, 2016 USD ($) Funds shares	Sep. 30, 2015 USD ($) shares	Sep. 23, 2016 USD ($)
Partnership Organization and Basis of Presentation [Line Items]
Number of Hennessy funds to which company provides investment advisory services \| Funds	16
Contractual expense ratio limitations termination date	Feb. 28, 2015
Unrealized gains	$ 600	$ 600
Number of mutual funds \| Funds	23
Management contracts impairment amount	$ 0	$ 0
Effective tax rates	36.30%	39.40%
Common stock equivalents (anti-dilutive) excluded from per share calculation \| shares	0	0
Shares available for issuance	50.00%
Share based compensation percentage criteria description	More than 50% of the outstanding shares
Shares grant period	10 years
Maximum aggregate fair market value of shares	$ 100,000
Westport Fund and Westport Select Cap Fund [Member]
Partnership Organization and Basis of Presentation [Line Items]
Acquisition of Westport Fund and the Westport Select Cap Fund			$ 435,000,000
Cash paid	11,300,000
Total capitalized costs related to purchase	$ 11,400,000
Minimum [Member]
Partnership Organization and Basis of Presentation [Line Items]
Estimated useful lives of assets	1 year
Percentage of exercise price of fair value	110.00%
Maximum [Member]
Partnership Organization and Basis of Presentation [Line Items]
Estimated useful lives of assets	10 years
Shares grant period	10 years
Maximum Vesting Period	5 years
Restricted Stock Units (RSUs) [Member]
Partnership Organization and Basis of Presentation [Line Items]
Maximum Vesting Period	4 years
Rate of restricted stock units vest under plan	25.00%
Granted, Number of Restricted Share Units \| shares	88,200	182,500
Compensation expense related to non-vested awards not yet recognized	$ 6,142,000
Weighted-average vesting period for compensation expenses not yet recognized	2 years 10 months 24 days
Stock Appreciation Right [Member]
Partnership Organization and Basis of Presentation [Line Items]
Aggregate number of shares \| shares	50,000
Incentive Stock Option Plan [Member] \| Minimum [Member]
Partnership Organization and Basis of Presentation [Line Items]
Percentage of shareholder ownership to meet incentive stock option	10.00%
2013 Omnibus Incentive Plan [Member]
Partnership Organization and Basis of Presentation [Line Items]
Number of options available for grant \| shares	2,553,990