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401(k) Plan (Details) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Retirement Benefits [Abstract]
Employee contribution, percentage of annual salary	100.00%
Employee contribution, maximum allowable contribution	$ 58,000
Service period for participation eligibility	30 days
Service period for eligibility of profit sharing or matching contributions	1 year
Employer matching contribution percent	100.00%
Percent of employees' gross pay	4.00%
Profit sharing contribution, vesting schedule (in years)	6 years
Profit sharing contribution, percent	7.00%
Company contributions to plan	$ 9,905,000	$ 8,333,000	$ 6,920,000

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Amount of cost for defined contribution plan.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

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