Retirement Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Retirement Benefits [Abstract]
Service cost	$ 75	$ 63	$ 149	$ 126
Interest cost	264	239	528	479
Expected return on plan assets	(393)	(401)	(787)	(803)
Amortization of net loss	107	161	215	323
Net periodic cost	$ 53	$ 62	$ 105	$ 125