Stock-Based Compensation - Summary of Restricted Share and Performance-Based Stock Award Activity (Details) - $ / shares	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2020	Sep. 30, 2019
Restricted shares
Common Shares
Shares, beginning of fiscal year (in shares)		190,805	163,287
Granted (in shares)	134,185		106,753
Vested (in shares)	(83,909)		(76,210)
Forfeited (in shares)	(3,109)		(3,025)
Canceled (in shares)	0		0
Shares, end of period (in shares)	237,972	237,972	190,805
Vested, but not issuable at end of period (in shares)	62,992	62,992	50,770
Weighted-Average Grant Date Fair Value
Shares, beginning of fiscal year (in dollars per share)		$ 37.20	$ 37.86
Granted (in dollars per share)	$ 32.34		37.27
Vested (in dollars per share)	38.61		38.64
Forfeited (in dollars per share)	36.61		38.67
Canceled (in dollars per share)	0		0
Shares, end of period (in dollars per share)	33.97	33.97	37.20
Vested, but not issuable at end of period (in dollars per share)	$ 33.98	$ 33.98	$ 33.88
Performance shares
Common Shares
Shares, beginning of fiscal year (in shares)		173,332	175,196
Granted (in shares)		(48,753)	60,583
Vested (in shares)		(54,861)	(59,937)
Forfeited (in shares)		(3,732)	(2,510)
Canceled (in shares)		0	0
Shares, end of period (in shares)	65,986	65,986	173,332
Vested, but not issuable at end of period (in shares)	5,612	5,612	5,612
Weighted-Average Grant Date Fair Value
Shares, beginning of fiscal year (in dollars per share)		$ 38.50	$ 36.29
Granted (in dollars per share)		(49.22)	32.77
Vested (in dollars per share)		39.43	30.79
Forfeited (in dollars per share)		38.14	39.25
Canceled (in dollars per share)		0	0
Shares, end of period (in dollars per share)	$ 34.61	34.61	38.50
Vested, but not issuable at end of period (in dollars per share)	$ 18.00	$ 18.00	$ 18.00