Loans Receivable and Related Allowance for Loan Losses (10) (Detail) $ in Thousands	3 Months Ended		6 Months Ended	12 Months Ended
	Mar. 31, 2021 USD ($) Number	Mar. 31, 2020 Number	Mar. 31, 2021 USD ($) Number	Sep. 30, 2020 USD ($) Number
Financing Receivable, Impaired [Line Items]
Number of Loans | Number	0	0	12	43
Loan Deferment Exposure	$ 62,398		$ 62,398	$ 144,785
Gross Loans	$ 986,428		$ 986,428	$ 1,039,001
Percentage of Gross Loans on Deferral	6.33%		6.33%	13.94%
Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Number of Loans | Number			2	10
Loan Deferment Exposure	$ 212		$ 212	$ 5,547
Gross Loans	$ 94,706		$ 94,706	$ 116,584
Percentage of Gross Loans on Deferral	0.02%		0.02%	0.53%
Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Number of Loans | Number			1	5
Loan Deferment Exposure	$ 240		$ 240	$ 1,288
Gross Loans	$ 218,165		$ 218,165	$ 242,090
Percentage of Gross Loans on Deferral	0.02%		0.02%	0.12%
Construction and Development - Residential and Commercial Receivables [Member]
Financing Receivable, Impaired [Line Items]
Gross Loans	$ 76,257		$ 76,257	$ 65,703
Percentage of Gross Loans on Deferral	0.00%		0.00%	0.00%
Construction and Development - Land Receivable [Member]
Financing Receivable, Impaired [Line Items]
Gross Loans	$ 3,596		$ 3,596	$ 3,110
Percentage of Gross Loans on Deferral	0.00%		0.00%	0.00%
Construction And Development Receivable [Member]
Financing Receivable, Impaired [Line Items]
Gross Loans	$ 79,853		$ 79,853	$ 68,813
Percentage of Gross Loans on Deferral	0.00%		0.00%	0.00%
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Number of Loans | Number			7	21
Loan Deferment Exposure	$ 61,858		$ 61,858	$ 131,348
Gross Loans	$ 482,611		$ 482,611	$ 495,398
Percentage of Gross Loans on Deferral	6.28%		6.28%	12.64%
Commercial Farmland [Member]
Financing Receivable, Impaired [Line Items]
Number of Loans | Number				1
Loan Deferment Exposure				$ 2,288
Gross Loans	$ 7,344		$ 7,344	$ 7,517
Percentage of Gross Loans on Deferral	0.00%		0.00%	0.22%
Commercial Multi Family Receivable [Member]
Financing Receivable, Impaired [Line Items]
Number of Loans | Number				2
Loan Deferment Exposure				$ 3,718
Gross Loans	$ 67,122		$ 67,122	$ 67,767
Percentage of Gross Loans on Deferral	0.00%		0.00%	0.36%
Commercial - Other Receivable [Member]
Financing Receivable, Impaired [Line Items]
Gross Loans	$ 9,927		$ 9,927	$ 10,142
Percentage of Gross Loans on Deferral	0.00%		0.00%	0.00%
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Number of Loans | Number			9	34
Loan Deferment Exposure	$ 62,070		$ 62,070	$ 142,901
Gross Loans	$ 661,710		$ 661,710	$ 697,408
Percentage of Gross Loans on Deferral	6.30%		6.30%	13.75%
Consumer - Home Equity Lines of Credit [Member]
Financing Receivable, Impaired [Line Items]
Number of Loans | Number				3
Loan Deferment Exposure				$ 579
Gross Loans	$ 15,936		$ 15,936	$ 17,128
Percentage of Gross Loans on Deferral	0.00%		0.00%	0.06%
Consumer - Second Mortgages Receivable [Member]
Financing Receivable, Impaired [Line Items]
Number of Loans | Number			2	1
Loan Deferment Exposure	$ 88		$ 88	$ 17
Gross Loans	$ 8,114		$ 8,114	$ 10,711
Percentage of Gross Loans on Deferral	0.01%		0.01%	0.00%
Consumer - Other Receivable [Member]
Financing Receivable, Impaired [Line Items]
Gross Loans	$ 2,650		$ 2,650	$ 2,851
Percentage of Gross Loans on Deferral	0.00%		0.00%	0.00%
Consumer Receivable [Member]
Financing Receivable, Impaired [Line Items]
Number of Loans | Number			2	4
Loan Deferment Exposure	$ 88		$ 88	$ 596
Gross Loans	$ 26,700		$ 26,700	$ 30,690
Percentage of Gross Loans on Deferral	0.01%		0.01%	0.06%