Retirement Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Retirement Benefits [Abstract]
Service cost	$ 85	$ 75	$ 170	$ 149
Interest cost	208	264	416	528
Expected return on plan assets	(363)	(393)	(727)	(787)
Amortization of net loss	188	107	376	215
Net periodic cost	$ 118	$ 53	$ 235	$ 105