Earnings Per Share - Composition of the Weighted-Average Common Shares (Denominator) Used in the Basic and Diluted Earnings per Share Computation (Detail) - shares	3 Months Ended								12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Weighted-average common shares outstanding									18,133,095	18,133,095	18,133,095
Average treasury stock shares									(6,769,423)	(6,682,911)	(6,284,870)
Average unearned ESOP shares									(927,908)	(973,168)	(1,018,444)
Average unearned nonvested shares									(37,276)	(22,560)	(12,351)
Weighted-average common shares and common stock equivalents used to calculate basic earnings per share	10,456,404	10,426,304	10,385,154	10,364,425	10,426,195	10,431,461	10,442,310	10,516,097	10,398,488	10,454,456	10,817,430
Additional common stock equivalents (nonvested stock) used to calculate diluted earnings per share										9,787	3,485
Additional common stock equivalents (stock options) used to calculate diluted earnings per share									120,580	78,887
Weighted-average common shares and common stock equivalents used to calculate diluted earnings per share	10,579,314	10,553,138	10,524,697	10,535,573	10,550,243	10,565,123	10,521,147	10,516,097	10,519,068	10,543,130	10,820,915