Earning Per Share Data - Basic and Diluted Earnings Per Share (Detail) - USD ($)	3 Months Ended				6 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 7,460,000	$ 313,000	$ 3,764,000	$ 2,346,000	$ 7,773,000	$ 6,110,000
Common Shares:
Weighted average common shares outstanding	14,541,000		14,482,000		14,541,000	14,470,000
Effect of dilutive stock options	167,000		246,000		164,000	255,000
Diluted shares outstanding	14,708,000		14,728,000		14,705,000	14,725,000
Basic:
Net earnings per share	$ 0.51		$ 0.26		$ 0.53	$ 0.42
Diluted:
Net earnings per share	$ 0.51		$ 0.26		$ 0.53	$ 0.41