Inventories - Schedule Of Retrospective Application of Change In Accounting Method Of Inventory (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
ASSETS
Inventories, net	$ 25,366,000	$ 21,890,000	[1]
Prepaid expenses	499,000	1,348,000	[1]
LIABILITIES AND SHAREHOLDERS' EQUITY
Deferred and other income taxes	3,372,000	2,640,000	[1]
Retained earnings	141,897,000	131,701,000	[1]
Consolidated Income Statements
Cost of goods sold	58,917,000	71,818,000	[2]
Income before income tax expense	12,824,000	15,064,000	[2]
Income tax expense	2,628,000	2,370,000	[2]
Net income	$ 10,196,000	$ 12,694,000	[3]
Basic earnings per common share	$ 0.70	$ 0.88	[2]
Diluted earnings per common share	$ 0.69	$ 0.86	[2]
Consolidated Statements of Cash Flows
Net income	$ 10,196,000	$ 12,694,000	[2]
Deferred and other income taxes	(732,000)	(262,000)	[2]
Inventories	3,476,000	1,702,000	[2]
Accrued expenses	$ 575,000	(357,000)	[2]
Previously Reported [Member]
ASSETS
Inventories, net		18,214,000
Prepaid expenses		1,904,000
LIABILITIES AND SHAREHOLDERS' EQUITY
Deferred and other income taxes		2,358,000
Retained earnings		128,863,000
Consolidated Income Statements
Cost of goods sold		71,993,000
Income before income tax expense		14,889,000
Income tax expense		2,325,000
Net income		$ 12,564,000
Basic earnings per common share		$ 0.87
Diluted earnings per common share		$ 0.85
Consolidated Statements of Cash Flows
Net income		$ 12,564,000
Deferred and other income taxes		757,000
Inventories		(1,527,000)
Prepaid expenses		(244,000)
Accrued expenses		(341,000)
Restatement Adjustment [Member]
ASSETS
Inventories, net		3,676,000
Prepaid expenses		(556,000)
LIABILITIES AND SHAREHOLDERS' EQUITY
Deferred and other income taxes		282,000
Retained earnings		2,838,000
Consolidated Income Statements
Cost of goods sold		(175,000)
Income before income tax expense		175,000
Income tax expense		45,000
Net income		$ 130,000
Basic earnings per common share		$ 0.01
Diluted earnings per common share		$ 0.01
Consolidated Statements of Cash Flows
Net income		$ 130,000
Deferred and other income taxes		(495,000)
Inventories		(175,000)
Prepaid expenses		556,000
Accrued expenses		(16,000)
As Reported Under FIFO [Member]
ASSETS
Inventories, net		21,890,000
Prepaid expenses		1,348,000
LIABILITIES AND SHAREHOLDERS' EQUITY
Deferred and other income taxes		2,640,000
Retained earnings		131,701,000
Consolidated Income Statements
Cost of goods sold		71,818,000
Income before income tax expense		15,064,000
Income tax expense		2,370,000
Net income		$ 12,694,000
Basic earnings per common share		$ 0.88
Diluted earnings per common share		$ 0.86
Consolidated Statements of Cash Flows
Net income		$ 12,694,000
Deferred and other income taxes		262,000
Inventories		(1,702,000)
Prepaid expenses		312,000
Accrued expenses		$ (357,000)

[1] The amounts as of September 30, 2018 have been adjusted to reflect the change in inventory accounting method, as described in Notes 1 and 2 to the Consolidated Financial Statements.

[2] The amounts for the year ended September 30, 2018 have been adjusted to reflect the change in inventory accounting method, as described in Notes 1 and 2 to the Consolidated Financial Statements.

[3] The balances as of September 30, 2017 and 2018, and the amounts for the year ended September 30, 2018, have been adjusted to reflect the change in inventory accounting method, as described in Notes 1 and 2 to the Consolidated Financial Statements.