Pension and Retirement Plans - Components of net periodic benefit costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Pension
Pension:
Interest cost	$ 63	$ 70	$ 124	$ 140
Expected return on plan assets	(99)	(74)	(196)	(148)
Amortization of:
Amortization of past service costs	2	2	4	4
Amortization of net gain (loss)	46	49	91	98
Net periodic benefit cost	12	47	23	94
Post Retirement
Pension:
Service cost	12	9	23	19
Interest cost	11	11	22	23
Amortization of:
Amortization of net gain (loss)	12	6	25	12
Net periodic benefit cost	35	26	70	54
U.S. | Pension
Pension:
Interest cost	2	4	5	8
Amortization of:
Amortization of net gain (loss)	1	1	2	2
Net periodic benefit cost	3	5	7	10
U.S. | Post Retirement
Pension:
Service cost	12	9	23	19
Interest cost	11	11	22	23
Amortization of:
Amortization of net gain (loss)	12	6	25	12
Net periodic benefit cost	35	26	70	54
U.K. | Pension
Pension:
Interest cost	61	66	119	132
Expected return on plan assets	(99)	(74)	(196)	(148)
Amortization of:
Amortization of past service costs	2	2	4	4
Amortization of net gain (loss)	45	48	89	96
Net periodic benefit cost	$ 9	$ 42	$ 16	$ 84