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	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	$ 186,260	$ 184,373
Total loans held for sale	15,920	9,952
Loans servicing rights	2,554	2,405	$ 1,746	$ 1,389
Residential mortgage loans held for sale	734,061	704,271
Derivative assets (included in other assets)	658	421
Derivative liabilities (included in other liabilities)	132	0
Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned	232
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	122
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	186,260	184,373
Derivative assets (included in other assets)	658	421
Derivative liabilities (included in other liabilities)	132
Fair Value, Measurements, Recurring | Residential Mortgage Loans Held For Sale Fair Value Option Elected [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage loans held for sale	15,920	9,952
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	24,193	31,130
Fair Value, Measurements, Recurring | Agency CMO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	12,049	10,441
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	1,492	1,579
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	1,589	1,884
Fair Value, Measurements, Recurring | SBA Certificates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	1,318	1,351
Fair Value, Measurements, Recurring | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	145,619	137,988
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	12,711	12,816
Loans servicing rights	2,554	2,405
Total other real estate owned		103
Fair Value, Measurements, Nonrecurring | Residential real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	4,922	5,100
Fair Value, Measurements, Nonrecurring | Commercial real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	7,194	7,227
Total other real estate owned	110
Fair Value, Measurements, Nonrecurring | Commercial business
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	294	231
Fair Value, Measurements, Nonrecurring | Consumer
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	301	231
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	27
Fair Value, Measurements, Nonrecurring | Small Business Administration Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total loans held for sale	22,032	21,659
Fair Value, Measurements, Nonrecurring | Residential mortgage loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned		103
Fair Value, Measurements, Nonrecurring | Residential Mortgage Loans Held For Sale Fair Value Option Not Elected [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage loans held for sale	0	514
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Loans servicing rights	0	0
Residential mortgage loans held for sale	0	0
Derivative assets (included in other assets)	0	0
Derivative liabilities (included in other liabilities)	0
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
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
Level 1 | Residential mortgage loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage loans held for sale	0	0
Level 1 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Derivative assets (included in other assets)	0	0
Derivative liabilities (included in other liabilities)	0
Level 1 | Fair Value, Measurements, Recurring | Residential Mortgage Loans Held For Sale Fair Value Option Elected [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage loans held 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 bonds
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 servicing rights	0	0
Total other real estate owned		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
Total other real estate owned	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]
Total 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]
Total other real estate owned		0
Level 1 | Fair Value, Measurements, Nonrecurring | Residential Mortgage Loans Held For Sale Fair Value Option Not Elected [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage loans held for sale		0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	186,260	184,373
Loans servicing rights	0	0
Residential mortgage loans held for sale	0	0
Derivative assets (included in other assets)	0	41
Derivative liabilities (included in other liabilities)	132
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
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
Level 2 | Residential mortgage loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage loans held for sale	15,920	10,476
Level 2 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	186,260	184,373
Derivative assets (included in other assets)	0	41
Derivative liabilities (included in other liabilities)	132
Level 2 | Fair Value, Measurements, Recurring | Residential Mortgage Loans Held For Sale Fair Value Option Elected [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage loans held for sale	15,920	9,952
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	24,193	31,130
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	12,049	10,441
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	1,492	1,579
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	1,589	1,884
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	1,318	1,351
Level 2 | Fair Value, Measurements, Recurring | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	145,619	137,988
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 servicing rights	0	0
Total other real estate owned		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
Total other real estate owned	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]
Total loans held for sale	0	21,659
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]
Total other real estate owned		0
Level 2 | Fair Value, Measurements, Nonrecurring | Residential Mortgage Loans Held For Sale Fair Value Option Not Elected [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage loans held for sale		514
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Loans servicing rights	2,614	2,405
Residential mortgage loans held for sale	698,595	673,652
Derivative assets (included in other assets)	658	380
Derivative liabilities (included in other liabilities)	0
Level 3 | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total other real estate owned	232
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	122
Level 3 | Residential mortgage loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage loans held for sale	0	0
Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Derivative assets (included in other assets)	658	380
Derivative liabilities (included in other liabilities)	0
Level 3 | Fair Value, Measurements, Recurring | Residential Mortgage Loans Held For Sale Fair Value Option Elected [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage loans held for sale	0	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 bonds
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	12,711	12,816
Loans servicing rights	2,554	2,405
Total other real estate owned		103
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	4,922	5,100
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	7,194	7,227
Total other real estate owned	110
Level 3 | Fair Value, Measurements, Nonrecurring | Commercial business
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	294	231
Level 3 | Fair Value, Measurements, Nonrecurring | Consumer
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total impaired loans	301	231
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	0	27
Level 3 | Fair Value, Measurements, Nonrecurring | Small Business Administration Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total loans held for sale	$ 22,032	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]
Total other real estate owned		103
Level 3 | Fair Value, Measurements, Nonrecurring | Residential Mortgage Loans Held For Sale Fair Value Option Not Elected [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Residential mortgage loans held for sale		$ 0