Earnings per Share - EPS Reconciliation (Details) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 23,400,000.0	$ 22,700,000.0	$ 41,600,000	$ 15,800,000
Less: Net income allocated to participating securities	(400,000)	(300,000)	(700,000)	(300,000)
Net income allocated to common shareholders	$ 23,000,000	$ 22,400,000	$ 40,900,000	$ 15,500,000
Weighted average number of common shares outstanding	18,753,490	18,559,849	18,706,104	18,502,795
Dilutive potential common shares outstanding:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	251,303	299,484	293,785	333,418
Diluted weighted-average shares	19,004,793	18,859,333	18,999,889	18,836,213