Fair Value Measurements and Disclosures about Fair Value of Financial Instruments (Balances Of Financial Assets Measured At Fair Value On Recurring And Nonrecurring) (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	$ 5,819		$ 9,255
Total securities available for sale	178,019		174,493
Loans servicing rights	1,026	$ 783	310	$ 282	$ 156	$ 0
Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned	346		519
Residential real estate | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned	179		397
Commercial real estate | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned	167		122
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	5,819		9,255
Total securities available for sale	178,019		174,493
Fair Value, Measurements, Recurring | Agency bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale			1,032
Fair Value, Measurements, Recurring | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	39,340		47,405
Fair Value, Measurements, Recurring | Agency CMO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	14,235		16,095
Fair Value, Measurements, Recurring | Privately issued CMO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	2,059		2,652
Fair Value, Measurements, Recurring | Privately-issued ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	3,769		4,532
Fair Value, Measurements, Recurring | SBA Certificates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	1,050		1,227
Fair Value, Measurements, Recurring | Municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	117,566		101,550
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	10,570		11,313
Loans held for sale	24,970		5,471
Loans servicing rights	1,026		310
Fair Value, Measurements, Nonrecurring | Residential real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	4,400		4,299
Fair Value, Measurements, Nonrecurring | Commercial real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	5,464		6,298
Fair Value, Measurements, Nonrecurring | Commercial business
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	198		231
Fair Value, Measurements, Nonrecurring | Consumer
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	194		244
Fair Value, Measurements, Nonrecurring | Land and Land Development [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	314		241
Fair Value, Measurements, Nonrecurring | Small Business Administration Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	24,215		5,087
Fair Value, Measurements, Nonrecurring | Residential mortgage loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	755		384
Level 1 | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned	0		0
Level 1 | Residential real estate | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned	0		0
Level 1 | Commercial real estate | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned	0		0
Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	0		0
Total securities available for sale	0		0
Level 1 | Fair Value, Measurements, Recurring | Agency bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale			0
Level 1 | Fair Value, Measurements, Recurring | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0		0
Level 1 | Fair Value, Measurements, Recurring | Agency CMO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0		0
Level 1 | Fair Value, Measurements, Recurring | Privately issued CMO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0		0
Level 1 | Fair Value, Measurements, Recurring | Privately-issued ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0		0
Level 1 | Fair Value, Measurements, Recurring | SBA Certificates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0		0
Level 1 | Fair Value, Measurements, Recurring | Municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0		0
Level 1 | Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	0		0
Loans held for sale	0		0
Loans servicing rights	0		0
Level 1 | Fair Value, Measurements, Nonrecurring | Residential real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	0		0
Level 1 | Fair Value, Measurements, Nonrecurring | Commercial real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	0		0
Level 1 | Fair Value, Measurements, Nonrecurring | Commercial business
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	0		0
Level 1 | Fair Value, Measurements, Nonrecurring | Consumer
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	0		0
Level 1 | Fair Value, Measurements, Nonrecurring | Land and Land Development [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	0		0
Level 1 | Fair Value, Measurements, Nonrecurring | Small Business Administration Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	0		0
Level 1 | Fair Value, Measurements, Nonrecurring | Residential mortgage loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	0		0
Level 2 | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned	0		0
Level 2 | Residential real estate | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned	0		0
Level 2 | Commercial real estate | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned	0		0
Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	5,819		9,255
Total securities available for sale	178,019		174,493
Level 2 | Fair Value, Measurements, Recurring | Agency bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale			1,032
Level 2 | Fair Value, Measurements, Recurring | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	39,340		47,405
Level 2 | Fair Value, Measurements, Recurring | Agency CMO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	14,235		16,095
Level 2 | Fair Value, Measurements, Recurring | Privately issued CMO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	2,059		2,652
Level 2 | Fair Value, Measurements, Recurring | Privately-issued ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	3,769		4,532
Level 2 | Fair Value, Measurements, Recurring | SBA Certificates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	1,050		1,227
Level 2 | Fair Value, Measurements, Recurring | Municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	117,566		101,550
Level 2 | Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	0		0
Loans held for sale	24,970		5,471
Loans servicing rights	0		0
Level 2 | Fair Value, Measurements, Nonrecurring | Residential real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	0		0
Level 2 | Fair Value, Measurements, Nonrecurring | Commercial real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	0		0
Level 2 | Fair Value, Measurements, Nonrecurring | Commercial business
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	0		0
Level 2 | Fair Value, Measurements, Nonrecurring | Consumer
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	0		0
Level 2 | Fair Value, Measurements, Nonrecurring | Land and Land Development [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	0		0
Level 2 | Fair Value, Measurements, Nonrecurring | Small Business Administration Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	24,215		5,087
Level 2 | Fair Value, Measurements, Nonrecurring | Residential mortgage loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	755		384
Level 3 | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned	346		519
Level 3 | Residential real estate | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned	179		397
Level 3 | Commercial real estate | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned	167		122
Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	0		0
Total securities available for sale	0		0
Level 3 | Fair Value, Measurements, Recurring | Agency bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale			0
Level 3 | Fair Value, Measurements, Recurring | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0		0
Level 3 | Fair Value, Measurements, Recurring | Agency CMO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0		0
Level 3 | Fair Value, Measurements, Recurring | Privately issued CMO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0		0
Level 3 | Fair Value, Measurements, Recurring | Privately-issued ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0		0
Level 3 | Fair Value, Measurements, Recurring | SBA Certificates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0		0
Level 3 | Fair Value, Measurements, Recurring | Municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0		0
Level 3 | Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	10,570		11,313
Loans held for sale	0		0
Loans servicing rights	1,026		310
Level 3 | Fair Value, Measurements, Nonrecurring | Residential real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	4,400		4,299
Level 3 | Fair Value, Measurements, Nonrecurring | Commercial real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	5,464		6,298
Level 3 | Fair Value, Measurements, Nonrecurring | Commercial business
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	198		231
Level 3 | Fair Value, Measurements, Nonrecurring | Consumer
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	194		244
Level 3 | Fair Value, Measurements, Nonrecurring | Land and Land Development [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	314		241
Level 3 | Fair Value, Measurements, Nonrecurring | Small Business Administration Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	0		0
Level 3 | Fair Value, Measurements, Nonrecurring | Residential mortgage loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	$ 0		$ 0