Employee Benefits - Additional Information (Detail) - USD ($)								12 Months Ended
	Mar. 29, 2017	Dec. 13, 2016	Mar. 04, 2016	May 20, 2015	Jul. 22, 2014	Apr. 01, 2013	May 23, 2008	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Compensation Related Costs Disclosure [Line Items]
Service Period								1 year
Age of Employee								21 years
Acquired Shares of the Company's Stock								1,358,472
Outstanding loan interest								3.75%
Annual payment of principal and interest								$ 718,000
Recognized ESOP expense								$ 686,000	$ 612,000	$ 561,000
Stock option granted								0
Option vesting period								5 years
Option expiration period								10 years
Share-based compensation expense								$ 331,000	192,000	113,000
Defined benefit plan curtailment								4,579,000
Reduction in accumulated other comprehensive loss								3,022,000,000
Accumulated benefit obligation								18,598,000	20,361,000
Estimated net loss								0
Expected contribution of bank								0
Allocated share based compensation expense								$ 251,000
Supplemental executive retirement plan minimum period								No less than 192 months
Estimated present value of benefits under plan								$ 1,600,000	1.2
Supplemental executive retirement plan discounting rate for present value calculation								6.00%
Expense related to supplemental executive retirement plan								$ 447,000	413,000	0
Equity [Member]
Compensation Related Costs Disclosure [Line Items]
Target allocation of cash and fixed income								65.00%
Cash and Fixed Income [Member]
Compensation Related Costs Disclosure [Line Items]
Target allocation of cash and fixed income								35.00%
Equity Incentive Plan [Member]
Compensation Related Costs Disclosure [Line Items]
Common stock issuance, Grant								2,377,326
2016 Plan [Member]
Compensation Related Costs Disclosure [Line Items]
Common stock issuance, Grant								250,000
Stock Option [Member]
Compensation Related Costs Disclosure [Line Items]
Number of available shares								1,698,090
Restricted Stock [Member]
Compensation Related Costs Disclosure [Line Items]
Number of available shares								679,236
Restricted stock granted	3,296	20,675	23,491	21,843	19,880	30,000	590,320
Share-based compensation expense								$ 318,000	$ 193,000	$ 95,000
Restricted Stock [Member] | 2013 [Member]
Compensation Related Costs Disclosure [Line Items]
Restricted shares vesting period								18 months
Restricted Stock [Member] | 2014 [Member]
Compensation Related Costs Disclosure [Line Items]
Restricted shares vesting period								39 months
Restricted Stock [Member] | 2015 [Member]
Compensation Related Costs Disclosure [Line Items]
Restricted shares vesting period								40 months
Outstanding nonvested restricted stock								82,000
Remaining vesting periods								1 year
Restricted Stock [Member] | March 4, 2016 [Member]
Compensation Related Costs Disclosure [Line Items]
Restricted shares vesting period								43 months
Restricted Stock [Member] | December 13, 2016 [Member]
Compensation Related Costs Disclosure [Line Items]
Restricted shares vesting period								46 months
Restricted Stock [Member] | March 29, 2017 [Member] | Tranche One [Member]
Compensation Related Costs Disclosure [Line Items]
Restricted shares vesting period								42 months
Restricted shares vested, Number of shares								1,296
Restricted Stock [Member] | March 29, 2017 [Member] | Tranche Two [Member]
Compensation Related Costs Disclosure [Line Items]
Restricted shares vesting period								18 months
Restricted shares vested, Number of shares								2,000
Restricted Stock [Member] | March 2016 [Member]
Compensation Related Costs Disclosure [Line Items]
Outstanding nonvested restricted stock								170,000
Remaining vesting periods								2 years
Restricted Stock [Member] | December 2016 [Member]
Compensation Related Costs Disclosure [Line Items]
Outstanding nonvested restricted stock								268,000
Remaining vesting periods								3 years
Restricted Stock [Member] | March 2017 [Member] | Tranche One [Member]
Compensation Related Costs Disclosure [Line Items]
Outstanding nonvested restricted stock								16,000
Expected future expense								$ 1,296
Remaining vesting periods								3 years
Expected future expense								$ (1,296)
Restricted Stock [Member] | March 2017 [Member] | Tranche Two [Member]
Compensation Related Costs Disclosure [Line Items]
Outstanding nonvested restricted stock								19,000
Expected future expense								$ 2,000
Remaining vesting periods								1 year
Expected future expense								$ (2,000)
Non Qualified Stock Option [Member]
Compensation Related Costs Disclosure [Line Items]
Stock option granted							1,140,469
Incentive Stock Option [Member]
Compensation Related Costs Disclosure [Line Items]
Stock option granted							317,910